Lost World

""The continental hinterland consists of deserts, jungles and rainforests. It also contains lost kingdoms of Amazonian princesses, volcanoes, elephants' graveyards, lost diamond mines, strange ruins covered in hieroglyphics and hidden plateaus where the reptilian monsters of a bygone era romp and play. On any reasonable map of the area there's barely room for the trees.""

- The Discworld Companion on the dark continent of Klatch

Named after The Lost World by Sir Arthur Conan Doyle, this is, naturally, a geographic location off all maps.

They are usually found in remote locations, such as the center of large and barely explored continents (usually Darkest Africa), the polar ice caps, or mysterious islands. They are often home to lost civilizations with amazing Lost Technology, or to prehistoric animals that have managed to survive unchanged—aside from the fact that they suddenly find humans delicious. Some Lost Worlds are almost ludicrously dangerous and populated by fearsome monsters, and still others are Magical Lands where All Myths Are True. Prone to being destroyed by volcanic eruptions, floods, quakes, and/or bombs at the end of the book/film/series, with the protagonists barely escaping.

No longer popular (or even credible) with the advent of satellite mapping and GPS. Most modern fictions that use this trope are set in the pre-satellite past. The Lost World has now been adapted to serve in even more mysterious places, such as outer space or deep underground. You are now much more likely to see a civilization thought long dead on an episode of Star Trek than on your modern action show.

Applied Phlebotinum is sometimes used to explain why the area has stayed lost into the modern era; it's contained in a Pocket Dimension, or was created by aliens as a nature preserve, or some such Hand Wave. Occasionally treated more seriously, as a venue for playing with alternate evolutionary pathways.

It's worth knowing that some elements of this have happened in Real Life, even recently. However, they certainly don't match the scale of a true Lost World. For example, you might have a tribe that has had no interaction with the outside world for hundreds of years, but not, say, an entire civilization.

Two frequent lost worlds are the Deserted Island and (in older works) Mysterious Antarctica. Often a key element in a Jungle Opera.

Anime and Manga

 * Cage of Eden takes place on an island populated with anachronistic monsters. Birds from fifty million years ago, wolves from ten thousand years ago...and of course, they all want to kill the humans.

Comic Books

 * The Marvel Universe distills this trope into a place known as the "Savage Land." It is a tropical jungle in the middle of Antarctica filled with strange creatures, prehistoric beasts, warrior tribes, incredible civilizations and other great pulpy stuff.
 * It was in fact created by aliens.
 * The DCU has "Gorilla City", with its own phlebotinum ("invisible force fields") used to hide it, and populated by telepathic apes. It's appeared on TV in both Super Friends and Justice League.
 * Cavewoman is supposedly set in the late Cretaceous (with the main character having arrived there by time travel) but everything can be found in the primal jungle from Stock Dinosaurs to giant snakes, hominids, yetis and... trolls. Plus, one of the issues is named "Pangaian Sea".
 * Another Lost World in The DCU is "Skartaris" (a world located within the hollow Earth, accessible through a portal in the Arctic wilderness), which is the setting of Mike Grell's The Warlord (though other DC Universe characters would visit there from time to time as well). An episode of Justice League Unlimited is set there.
 * Skartaris is named after the Volcano through which Jules Verne's adventurers made their Journey to the Center of the Earth.
 * Skartaris was retconned into being Another Dimension. It cannot actually exist within the DC Universe's Earth, which isn't hollow.
 * A third DCU example: Themyscira, also known as Paradise Island, home to Wonder Woman and the Amazons.
 * Retconned into being able to travel around the world and through time itself.
 * Not much of a retcon- see Wonder Woman's Silver Age adventures.
 * And a fourth: Dinosaur Island, the setting for The War That Time Forgot series. In New Frontier, Dinosaur Island turns out to be.
 * Marvel similarly had a dinosaur-inhabited island which Skull the Slayer tried to civilize while simultaneously fighting off an Alien Invasion.
 * This was actually Earth's distant past, accessed by a time warp created by aliens.
 * Likewise, Monster Island is the home of the Mole Man, a frequent foe of the Fantastic Four. Its location seems to fluctuate between the Bermuda Triangle and just off the coast of Japan, depending on writers' whims.
 * The Mole Man and his monsters have vast underground passageways all across the Earth. Quite possibly two Monster Islands?
 * The Turok comic book series which had a pre-Columbian Native American and his younger brother Andar who enter a lost valley and get trapped in it. They call the dinosaurs which they encounter "Honkers".
 * Definitely retconned into being Another Dimension.
 * Tintin discovered a lost pocket of the Inca civilisation in Prisoners of the Sun.
 * Alan Moore had, as part of his Tom Strong series, a Wild West town set atop a large mesa. It was ripped out of time and as an intended side effect, the people could not live without some alien fruit. Tom leaves them up there on the mountain, to use them as Redshirts later on. The existence of sat-imagery is not commented upon.
 * Donald Duck has used this trope so many times. Usually when Scrooge dragged Donald and his nephews along to search for treasures.
 * Franka finds one in a crater on a Phillipine island.

Film

 * King Kong's home, which is generally referred to as Skull Island. In the original film, the island was never named, although it's most recognizable feature, Skull Mountain, was named; likewise in the 70s remake, the only reference is to "the beach of the skull".
 * Doyle's The Lost World was adapted as a silent film in 1925, with effects by Willis O'Brien, who also worked on King Kong. The film was also adapted in 1960 (with Giant Lizards in Makeup playing Dinosaurs), 1992 (with its own sequel--with Handpuppet Dinosaurs) and 1998 (pilot for the above mentioned TV series).
 * '50s B Movie and Mystery Science Theater 3000 feature Lost Continent, starring Cesar Romero. And it sure took some finding.
 * The Jurassic Park films (a man-made example). The first sequel is actually titled The Lost World and its plot borrows a lot from Conan Doyle's novel.
 * Also subverted by this series. Both islands can be found on maps, and Isla Sorna is accessible by boat.
 * The Asylum's adaptation of the Burroughs novel (see below) The Land That Time Forgot features, naturally, The Land that Time Forgot, which is a sort of cosmic eddy.
 * Amicus Pictures also adapted the book into a movie in The Seventies. In that one the Land that Time Forgot is a perfectly normal lost continent with nothing cosmic about it (except maybe the way the animals reproduce).
 * Paradise Falls from Up is a partial invocation of this trope. It's not particularly hidden, as Carl and Russell are able to find it with little more than a lot of balloons and a pocket GPS navigator. On the other hand, the film implies that it has remained unsettled because
 * The Land Unknown (1957) has a US Navy helicopter in Mysterious Antarctica crashing into a misty crater populated by highly unconvincing dinosaurs.
 * Ice Age: Dawn of the Dinosaurs used one to fit dinosaurs into the post-extinction ice age: the dinosaurs survived in an underground lost world.
 * The lost cave complex in the 1956 film The Mole People, in which the titular creatures live. They are enslaved by Evil Albino Sumerians who arrived in the caves when escaping a flood thousands of years ago.
 * It is implied in the Super Mario Bros. movie that dinosaurs have escaped from the parallel dimension into our world and humans into theirs throughout history, which would make the parallel world a sort of "Lost World".
 * The Disney film Atlantis: The Lost Empire has the titular Atlantis.
 * The island in Sannikov Land, which in legends is warmed by a volcano and therefore can be inhabited by a tribe called the Onkilon despite being in the far north.
 * Unknown Island from 1948.
 * Lagos Island is a fictional island off the coast of Japan. It's subverted in that it can be accessed via plane or boat, but people generally don't live there due to the population of large carnivorous dinosaurs. Oh, and the island was hit by nuclear radiation mutating said dinosaurs into city-destroying monstrosities.

Literature

 * Neverland, from J.M. Barrie's Peter Pan.
 * Edgar Rice Burroughs created a number of Lost Worlds.
 * Pellucidar, the hollow-earth dinosaur habitat, had its own series, and included a crossover with Tarzan.
 * Tarzan also stumbles across a number of Lost Worlds in Africa. These include:
 * Opar, first introduced in The Return of Tarzan (1913). This lost city is the last remnant of the world-spanning empire of Atlantis.
 * The Valley of the Holy Sepulcher, in Tarzan, Lord of the Jungle (1928). This valley was settled by two quarreling groups of Crusaders in the twelfth century, one of which claimed to have achieved the Holy Grail and thus the Crusade, while the other denied it. The latter group founded the city of Nimmr at one end of the valley, blocking the path of retreat to England, while the former group founded the City of the Sepulcher at the other end, blocking the route to the Middle East. The two groups have long since ceased any serious efforts to leave the valley, and have come to various accommodations with one another for their own survival.
 * Caspak (aka Caprona), a Lost World within Mysterious Antarctica, the setting for the novel The Land That Time Forgot and its sequels.
 * The Lost Continent (originally known as Beyond Thirty) - the titular continent is Europe, in an Alternate History in which World War I never ended because eventually no organized government was left to make peace. The United States never entered the war, and in fact made laws forbidding any ship to cross certain lines of longitude (hence the original title).
 * The Lost World by Sir Arthur Conan Doyle is the Trope Namer.
 * Robert E Howard's Solomon Kane encountered some of these in Darkest Africa. In particular, "The Moon of Skulls" featured a lost city that is all that remains of a once-vast empire which began as an outpost of Atlantis.
 * In Atlas Shrugged, Galt's Gulch is hidden within the mountains of Colorado with Applied Phlebotinum. Its use as a sanctuary for embattled egoistic industrialists has a sort of Deus Ex Machina quality about it.
 * As mentioned in the quote above, Discworld is full of lost lands, mostly on the vaguely Asian continent of Klatch. Some of them are especially lost because they move about; these are called "brigadoons". It also had two mysterious and near-mythical continents, the Counterweight Continent and Ecksecksecksecks, both of which are now thoroughly (re)discovered (although the inhabitants might insist that they've (re)discovered the main setting of the books).
 * Jules Verne's Journey to The Center of The Earth
 * Several recent authors such as James Rollins or Jeff Long have followed Verne's example, placing their modern Lost World tales underground, to justify such places having gone undiscovered.
 * Dinotopia plays this trope about as straight as possible.
 * Doc Savage encountered several Lost Worlds, the most significant being the lost Mayan kingdom that provided him with the gold necessary to carry on his crusade. Several of these Lost Worlds are also El Dorados.
 * The Diamond as Big as the Ritz by F. Scott Fitzgerald is all about an isolated pocket of fantastic wealth hidden in Montana. It's been successfully hidden by its wealthy, urbane, and autocratic owners for generations - but by the time of the story airplane overflight becomes a problem ...
 * Henders Island from Fragment plays this so literally it hurts.
 * The Hy-yi-yi islands, home of the Snouters, are a Lost World without the ruins. Lots of goofy-looking critters, but for once they're not trying to kill you.
 * The "Peach-blossom Spring" under the pen of Tao Qian (Tao Yuanmíng, c365－427 AD): a fisherman stumbles upon a secluded village, where people dress anachronistically and are at peace with themselves. The villagers, at first fearful, warm up with the outsider and treat him with lavish hospitality. They recount how their ancestors are driven to seclusion by political strife, and have since lost contact with outside. The fisherman leaves a few days later, having been requested to keep his adventure a secret. Despite having marked his way out, he never finds the place again.
 * A Strange Manuscript Found in a Copper Cylinder by James De Mille is another early example.
 * Jane Gaskell's Atlan series centers on the adventures of a displaced princess exploring a civilized prehistoric world "before the continents had changed." The first novel, The Serpent, is primarily a Jungle Opera; its immediate sequel, The Dragon, ends with the heroine entering Atlantis (or Atlan, as the saga calls it); the third, Atlan, picks up when she becomes empress of the continent. The first two novels even include a bibliography of (in some cases, discredited) research materials.
 * In the original book The Wonderful Wizard of Oz by L Frank Baum, the Land of Oz is a remote country that's surrounded by a vast, unpassable desert, keeping it isolated from the rest of the world. Sequel novels would establish that there were several other "fairy countries" bordering Oz's desert, all located on an unnamed continent somewhere in "the Nonestic Ocean". Baum was never clear about what region of the world this was supposed to be in, though a popular fan theory places it somewhere near Australia. Anyway, one of the sequels had a magic spell make Oz and its neighbors invisible to the outside world and reachable only through magic, so this became something of a moot point.
 * The Alcatraz Series of books takes this trope Up to Eleven: something like half the Earth's surface is made up of Lost Worlds called the Free Kingdoms where all sorts of magical and nonsensical things exist. They only go unnoticed because almost all the world's books, maps, and other sources of information are controlled by an ancient conspiracy of Evil Librarians who don't want you to learn the truth.

Live Action TV

 * Gilligans Island
 * The Land of the Lost
 * The various places encountered in the Bermuda Triangle by the characters of 1977's The Fantastic Journey.
 * A 1999-2002 series based on the titular story was called Sir Arthur Conan Doyles the Lost World.
 * The Lost World was also adapted as an A&E miniseries, in association with the Walking With Dinosaurs guys, starring Bob Hoskins, James Fox, and Peter Falk. It was a bit more faithful to the source, but - more importantly - the deviations they made were actually effective.
 * As stated above, Lost's Island would certainly fit this trope.
 * For those curious, it can't be found by normal means because it's constantly moving, possibly invisible and has a barrier around it so that if you don't go in at exactly the right bearing you'll become unstuck in time and likely die.
 * Most of the above conditions (the time warping and constantly moving parts in particular) were inadvertently caused by Ben . Before and after that event, there are other ways to get into the island, like through a submarine or helicopter. Still, regardless of the method, they all share the same problem with being impossible to enter or escape without a very specific coordinates to squeeze through the barrier.
 * Journey to the Beginning of Time, a Czech film that was syndicated to American TV, most notably on Garfield Goose And Friends.
 * The Danger Island segment from The Banana Splits.
 * Sanctuary has Hollow Earth, a subterranean city with incredible technology.
 * The city of Praxis was built deep underground nearly 8000 years ago by humans and abnormals fleeing from a vampire-occupied Earth. Since then they have been steadily progressing their technology without any major wars or religious strife.
 * Unfortunately,.
 * Wherever the hell Tower Prep is. It gets sent into this territory because it is full of flora and fauna that shouldn't coexist near each other, and the constellations don't match up with anywhere in North America.
 * Kinkao in Pair of Kings.
 * The Danger 5 episode "Lizard Soldiers of the Third Reich" has Joseph Mengele performing sinister experiments in a Lost World tropical plateau in Antarctica where dinosaurs, dinosaur-men, jazz-loving ape-men, and Nubile Savage women coexist. After Danger 5 arrives there, we receive a ludicrously nonsensical explanation for how the plateau has been isolated for 65 million years.

Mythology

 * Atlantis, the mythology of which at least predates Plato. A small continent made of seven concentric rings that allegedly sunk beneath the ocean. The Ur-example of literally countless lost, missing, or floating continents in Western culture.
 * The continent of Mu.
 * Shambala (sometimes Anglicized as Shangri-la,) a retreat somewhere in the Himalayas that's home to advanced technology and many demi-gods and saints.
 * Although it is widely considered to be more like a metaphoral "state" and not a physical place.
 * Lemuria, which was believed to be somewhere in the Pacific.
 * The Ghostapo (Nazi occultists) believed, among other things, that the Earth was a hollow sphere with a second sun in the center. Another civilization thrived in the inner Earth which could be accessed through a giant hole in the polar cap. Predates the Nazis though; an old alchemical aphorism states: Visita interiora terrae rectificando invenies occultem lapidem. (Visit the interior of the Earth to find the Philosopher's Stone.) This goes back at least to the period of The Chymical Wedding Of Christian Rosenkreuz.
 * Actually, the Hollow Earth theory wasn't just held as true by the Ghostapo, it was a very popular theory when it was introduced. It explained the subtle magnetic changes that the Earth experienced, and why Magnetic North sometimes changes. Combined with the fact that few people had ever been to either of the poles...
 * The lost oasis of Zerzura, supposedly a lush, verdant valley hidden somewhere in the Sahara.

Tabletop Games

 * Lands of Mystery, a supplement for the 1980's pulp game Justice Inc., was all about gaming in a Lost World setting. About half the book was taken up with Zorandar, a setting/campaign that had everything from dinosaurs to a lost Roman colony.
 * The Dungeons and Dragons game-setting of Mystara has a long history with this trope, featured in such classic adventures as "Isle of Dread" or "Night's Dark Terror". The Hollow World boxed set converted the interior of the planet into a massive Lost World a la Pellucidar, chock full of prehistoric creatures and lost civilizations.
 * The Zendikar setting in Magic the Gathering is an entire plane of this, complete with mystical artifacts and horrible death at every turn for everyone from Goblins to planeswalkers.
 * Spirit of the Century readily embraces this possibility due to its strong 1920s era pulp foundation. While no such places are directly described in too much detail, it's suggested that several exist in Darkest Africa (most notably, the kinds of places where Gorilla Khan's will is law) and there's a small hint of a lead for a Game Master to potentially follow about a journey to the Earth's core being planned in the sample adventure provided in the book.
 * The titular Hollow Earth of Hollow Earth Expedition is all about this trope, featuring never ending jungle, lost civilizations, dinosaurs, and increased healing rates.
 * Secrets of the Surface World supplement. One of these exists on a plateau in the Amazon rain forest. A British expedition reached it and returned, without any proof of their findings but with a fortune in uncut diamonds (a Shout Out to Sir Arthur Conan Doyle's novel The Lost World). There's a hint that the plateau connects to the Hollow Earth mentioned above.
 * Pathfinder has the Vaults of Orv deep below the surface of Golarion. One illustration has a giant Tyrannosaurus fighting an eldritch abomination in a jungle.

Theatre

 * The musical Brigadoon has its eponymous town surrounded by a mysterious fog in the Scottish highlands. The two American hunters who stumble upon it ask why there is no Brigadoon on the map, and eventually get a good answer: the town and its inhabitants vanished in an 18th century miracle, and only reappear for one day every hundred years.

Video Games

 * Earthbound has the aptly named Lost Underworld, an enormous underground cave. Unlike other areas of the game, the camera is zoomed out and your party is dwarfed by the jungle and gigantic carnivorous dinosaurs.
 * Ultima loves this trope almost as much as DC Comics:
 * In Ultima III and VII Part One, the legendary island of Ambrosia. Particularly odd because in the latter case it would seem to be in the way of shipping.
 * In Ultima V, a cavernous Underworld complete with shipwrecked sailor and lost expedition. In VI we learn that there's an entire civilization even deeper underground.
 * Worlds of Ultima: Savage Empire is set in Eoden, a copy of Doyle's Lost World complete with lost tribes, dinosaurs, and a "Dr. Livingstone, I presume" moment.
 * In Ultima VII Part Two: Serpent Isle, Serpent Isle has been missing from the maps since the end of the first game.
 * The "Lost World" bonus regions in the second and third installments of the Donkey Kong Country series.
 * Gaia's Navel in Chrono Cross is at the center of an inaccessable island (you have to be flown there). It's basically 65,000,000 B.C. from Chrono Trigger in the modern day - it even has a younger Expy of Ayla, Leah, who joins your party.
 * Pokémon Mystery Dungeon 2: Explorers of Time/Darkness features one of these in the penultimate level, the aptly-named Hidden Land. The Hidden Land is so-called because it is only exists within a split second of time, meaning that time must be stopped before it can be visited.
 * Un'Goro Crater of World of Warcraft.
 * The Sholazar Basin in Northrend also qualifies.
 * The Turok FPS videogame series, which were loosely based on the comic book, although the player character is a modern day Native American who gains access to modern weapons during the course of the game.
 * See above, the player character rampages through the 'Lost World' valley (among other settings) that the original comics were set in.
 * The DS port of Chrono Trigger adds the Lost Sanctum, which allows a village of reptites to survive at least until the middle ages. Inside of a mountain, so it's somewhat understandable that no one can find it.
 * The "Lost World" level in Sonic Adventure, located in the middle of the Mystic Jungle.
 * Explained as actually being in the ancient past - Tikal (shown as a funny glowing ball of light during most of the game) keeps sending characters to the past to try and explain why the mysterious being "Chaos" is a threat and how it can be stopped. Sometimes those characters stick around too long, end up in an oddly large temple, and are forced to find their way out (and in Knuckles' case, a few shards of the Master Emerald somehow made it there, despite the fact it was shattered only a few days ago, not 4,000 years ago).
 * Well, the levels themselves aren't actually in the past, but the characters do get transported there after completing them.
 * For that matter, Angel Island usually has elements of this. Being suspended in the sky by the power of the Master Emerald helps.
 * LaGias from the Elemental Lords portion of the Super Robot Wars mythos. Like Skartaris it's a bit inconsistant whether it's a true hollow earth or just a parallel universe that's accessable through portals hidden underground.
 * Eve Online recently jumped on this trope with wormholes that open up into "Sleeper" space. Along with several other races they were thought to be extinct. Wild Mass Guessing ranges from time loops to returns to Earth's galaxy though they are much more advanced now. Word of God has been ver silent on the matter. Also Earth itself qualifies due to the collapse of the Eve Gate.
 * Skies of Arcadia has Ixa'taka, a lost continent beyond the supposedly impassable South Ocean.
 * In Xenogears, many islands and whole continents of the world are missing from maps and unknown by most of the world's inhabitants, who have actually been programmed not to notice them through an infection called -the Limiter-. After the Limiter is lifted between disc one and disc two, disc two conveniently has a much more featured world map with lands the True Companions have not yet explored. It turns out that the missing lands were places that Solaris decreed that the planet's inhabitants should forget.
 * Halfway correct. Those continents/islands aren't visible because until the middle of the game, they weren't even on the same physical plane as the landmasses that the player is exploring. After the destruction of a certain dimensional generator, the space time barrier separating those landmasses that were 'on the other side' are now accessible. Note that an individual/ships can still pass from one 'plane' to the other with the proper technology; this is offhand referenced a few times throughout the game.
 * Dragon Quest VIII has one where you go to the dark world.
 * The Lost Planet series takes place on a literal Lost World, populated by giant creatures and hidden treasures.
 * Technically, in Dragon Quest III, you start in the lost world.
 * Dragon Quest VII has all but one island of the world be lost.
 * Return to Mysterious Island and its sequal play this fairly straight, the second game moreso than the first.
 * The Lost City of Z from Conduit 2.

Webcomics
"Father Time: I forget nothing! There's an occasional typographical error in temporal accounting but . . . Dinosaurs? Are those DINOSAURS!?! Someone get me temporal accounting! Stat!"
 * Zeetha of Girl Genius is a native of the Lost City of Skifander. Unfortunately, she was ill during the journey from Skifander to Europa, and doesn't remember the way back, and everyone else who might have a clue seems to be dead. Sometimes at Zeetha's hands.
 * Sluggy Freelance has The Valley That Time Forgot Lost In The Center Of The Earth, which seems to be populated entirely by Mole Men and mole-man eating dinosaurs. The "center of the earth" thing is just a name, though (it's actually a few hundred miles from the eath's core), as is the "valley" part (it's technically a cavern). The "that time forgot" part is literally true, however.

Western Animation

 * Disney's Atlantis the Lost Empire.
 * The Christmas Special Rudolph's Shiny New Year features a few variations of this trope in the Archipelago of Last Years. Where the old Anthropomorphic Personification of the year goes to retire, they choose an island to live in and Time Stands Still for everyone in that island. The island where One Million B.C. lives is Prehistoria of course, and a Ye Olden Days year lives on a Magical Land.
 * Subverted a bit in an episode of Duck Tales where the heroes find a Lost World region full of dinosaurs. However, not only do they escape it, but they have its location definitely recorded and make it an one of a kind of wildlife tourist attraction.
 * The episode "Tarzan and the Knights of Nimmr" of the 1970s Saturday morning cartoon Tarzan, Lord of the Jungle is loosely based on the book Tarzan, Lord of the Jungle (the setting was largely retained, but the characters and story were replaced with original characters). The two cities were merged into the single city of Nimmr, which had just been discovered by a balloonist at the beginning of the story.
 * Super Friends (1973-74) episode "The Mysterious Moles". Deep under the earth is the Bottomless Cave: a gigantic cavern filled with plants, lakes and dinosaurs.
 * Dino Boy in the Lost Valley, which aired along with Space Ghost. The title valley had cavemen, dinosaurs and other prehistoric creatures, and several lost civilizations.
 * Kong Island in Kong the Animated Series had dinosaurs, mammoths, an evil god with a harpy for a minion and the big ape himself. One of the episodes dealt with the origin of the island due to a time vortex caused by said evil god.