Lava Pit

Like a swimming pool, but more viscous and much hotter than water, and somewhat less inviting. Plus it's too dense to sink into and doesn't require you to periodically add chlorine or scoop out leaves. And it really doesn't matter if you don't wait an hour after eating before you jump in. A better simile, in fact, would be "not like a swimming pool." (cf.) Often used as a barrier rather than a trap proper, but with the right mechanisms and delivery chutes, a Lava Pit can make for a delightful surprise at the end of a long drop.

In urban or outer space settings (where flowing lava is hard to find), you can substitute a blast furnace, trash incinerator, open nuclear reactor, vat of molten metal, or really, anything that's very hot and lethal to anyone dropped in. This version may overlap with No OSHA Compliance.

The Lava Pit can only work as a slow descending trap thanks to Convection, Schmonvection - that wonderful law that says rising heat can't kill you and only touching the lava is fatal. Funnily enough, however, in many platform games, the lava seems to have sufficient viscosity for the player to launch him/herself into the air, shoes/backside on fire. You'll lose Hit Points, of course.

A subtrope of Lava Adds Awesome.

Anime And Manga

 * Yu-Gi-Oh! GX: Fubuki's Brainwashed Super-Powered Evil Side threatens Judai's roommates with one during their duel.
 * Mazinger Z: Several Mechanical Beasts were fought beside or over lava pits on the crater of a volcano -usually Mount Fuji-: Aeros B2 and B3, Holzon V3 -in one of the manga versions-, Debira X1... And in one episode, Kouji was dumped in one.
 * The climax of Noir takes place over a Lava Pit, in the mystical dimension in-between Spain and France. No, not Andorra.
 * Usually considered the best Pokémon battle in the anime, Charizard vs. Magmar took place over a lava pit.
 * In the Pokémon Colosseum games, stage 100 of Mt. Battle is on a platform that essentially floats on the lava pit in the crater of a volcano.
 * The Blackthorn Gym in Pokémon Gold and Silver and the remakes has lava. The solution to cross it and get to Clair differs between the original (Strength puzzle) and remakes (rotating floor).
 * In Transformers Headmasters, Sixshot captures Wheelie and threatens to drop him into a pit of acid in three hours unless the Autobots give him the secret of Fortress Maximus' sword. Said acid happened to look exactly like lava.
 * Also, in the Transformers comics smelting pits are generally used for particularly gruesome executions. If you like putting people into these, we know you're a creep.

Comic Books

 * Subverted (doubly) in the Legion of Super-Heroes comic. Sun Boy gained his powers when Doctor Zaxton Regulus locked him inside a nuclear reactor just before its activation. In a later issue, Regulus comments "I could have killed him when I had the chance. But no; I had to get theatrical!"
 * Alan Moore, naturally, takes this trope Up to Eleven in Tom Strong; during their first encounter, Paul Saveen, Strong's Arch Enemy, traps Tom in a pit about to be filled with Pholgestein, described as "heat in its liquid form".

Film

 * Seen in Indiana Jones and the Temple of Doom, with the variation that the unfortunate prisoner has his heart removed before being lowered, and the heart catches fire when the poor man is dipped into the lava.
 * The second Austin Powers movie features a Death Trap over a pit of lava. Doctor Evil seems to have a thing for magma.

Literature
"One presentation, movie, song, and puppet show later... Frodo: This sure is taking a long time."
 * Literary example: The Lord of the Rings, when Gollum falls with the One Ring into a lava pit inside Mt. Doom.
 * Parodied in One Ring to Rule Them All 2. Sauron ties up Frodo and Sam and slowly lowers them into Mt. Doom. Very slowly.


 * A variant in the James Bond novel You Only Live Twice: Blofeld threatens to leave Bond on top of a frequently erupting geyser unless he talks.
 * Chapter 9 of how to by Randall Munroe (the creator of xkcd) is "How to Build a Lava Moat". The chapter deconstructs the whole "lava pit" trope, while providing enough information to let the reader build a lava moat if he really wants to.

Live Action TV

 * Xena: Warrior Princess features on of these in "Sacrifice 2" with terrible consequences.
 * MacGyver found himself in several of these, including the aforementioned incinerator and reactor.
 * Parodied in The Basil Brush Show with a pool of Anil's chilli sauce.
 * An episode of Get Smart parodying The Prisoner of Zenda has Max swordfighting the bad guy next to a pit of molten metal. Max knocks bad guy's sword out of his hand into the pit; bad guy's flunky cries out "I'll get it!" and steps into the pit, never to resurface. Bad guy shrugs "Good help is so hard to find these days!"
 * In CSI: Miami, a guy falls into a pool filled with sodium hydroxide. Now remember your high school chemistry...

Tabletop Games

 * Dungeons and Dragons took this to it's logical extreme in Dungeonscape where stats are provided for sadistic Game Masters that want to have sharks that can swim (and breathe) in lava. One assumes that they must be fed on a diet of adventurers considering that fairly few other things can and will submerge themselves in molten lava.

Video Games

 * Portal's last test chamber includes a massive fire pit. GLaDOS tried lowering the main character into the fire, only to have her escape with portals.
 * In Resident Evil 4, you get to pull this trope on a miniboss. Easy way to help your chances of survival, given that there's two (Only Works Once for some reason). However, you lose any loot you would've gotten from that boss.
 * Resident Evil 5 does it one better: You get to do this on
 * Another example would be Resident Evil: The Darkside Chronicles, in which you defeat one of the Tyrants by knocking him into the lava in the blast furnace.
 * The video games Doom, Duke Nukem 3D, and Super Mario 64 all have some form of lava pit that you can walk across the rocks near it, or (with minor damage) touch it temporarily, but you only get serious injury if you stay in it for several seconds.
 * The Legend of Zelda shamelessly uses lava pits around the inevitable fire bosses (King Dodongo, Gleerok, Volvagia, Hot Head, etc.). Of interesting note is that in many cases the bosses themselves are vulnerable to the lava pit as soon as you incapacitate them or remove their armor.
 * In Majoras Mask, you can transform into a Goron, who apparently immune to lava (the flipside is that they easily freeze to death).
 * Bowser loves his lava pits, considering every single one of his many castles has one. In the first game, the most common method to beat him is to drop him into one.
 * Yoshi's Island DS also has lava pits, which kill Yoshi instantly if he falls in. A lava pit also plays a part in the battles against Big Guy the Stilted, where he must be pushed into one so Yoshi can damage him.
 * Not just the sequel, the original Yoshi's Island is a big fan of these as well.
 * Super Mario World has lava pools with slopes. It also has Palette Swapped chocolate pits in Chocolate Island.
 * In La-Mulana, several areas contain lava, which on top of draining your health like a mofo, is hard to swim around in, and disables your menus unless you have the Heatproof Case. Once you get the Ice Cape, you are completely invulnerable to lava. Also, one of the steps to the Bonus Level of Hell requires you to drop down several screens of a bottomless Lava Pit.
 * Tomb Raider Anniversary does this for the mutant boss in the final level before the final boss. You have to let the monster charge at you, pull off an bullet time shot so that it rolls over and over the edge, and then blast its fingers as it hangs on in order to drop it down a shaft with lava on the bottom.
 * A common Death Trap in the cave levels of Prince of Persia 2: The Shadow and the Flame. They were a good way of killing skeletons permanently.
 * The SNES version of PoP 1 had a level set inside a volcano(Convection, Schmonvection), and you start by falling in and have to grab onto a ledge.
 * Red Faction lets the player drop a levitating robot into a garbage incinerator to the same effect.
 * Pokémon Mystery Dungeon has lava areas in some levels. Fire Pokemon are able to move across them without taking damage.
 * In the Sonic the Hedgehog series, Marble, Hill Top, Lava Reef, and the Underground Zone all feature lots of lava (or magma) pits. Robotnik is very creative about incorporating them into his gauntlets of traps.
 * They even figure into some of the adaptations. For example, a climactic moment in the OVA.
 * I Wanna Be the Guy has entire floors covered with flamethrowers.
 * The Quake deathmatch level "Claustrophobopolis" had several lava pit death traps that players could spring on each other.
 * Ultima V, in the Evil Fortress, has a trapdoor in the floor that leads to another trapdoor, to another trapdoor, to another, to another, to another... then shows the character sprite in the "dead" position in a field of lava tiles.
 * Talorus in Ultima Underworld II has a MacGuffin in the center of a lava pit. You're supposed to complete a Broken Bridge quest to reach it, but it's easy enough to run across the lava and grab it while taking only minor damage.
 * In Dwarf Fortress, if you have access to the lava and magma-safe materials to manipulate it, you can build a variety of death traps, and magma furnaces removes the need for coal to smelt all metals except steel or in other fuel-consuming workshops (glass furnace, kiln, forge); without mine-able coal, you'd use more time and jobs to chop, haul and turn into charcoal wood. Aside of efficiency, no-fuel industry opens possibilities: it uses wood so sparsely (charcoal for steel, ash for soap and glass) that you may cover all needs with import if none grows at your site, or avoid woodcutting in dangerous biomes, or remain elf-friendly without any real inconvenience. The only issue is the creatures like Fire Imps, Magma Men or Magma Crabs living at said sites. On the upside, since magma stays hot forever (though "evaporates" like water when very shallow), a little magma reservoir under the furnace remains useful even if isolated. There's even an option in production of stone items to specify magma-safe rock (for mechanisms, hatches, etc).
 * More than that, magma is the preferred way for most DF players to deal with virtually any problem. Too much garbage? Melt it in lava ! Attacking hordes? Pump lava to the top of your tower, and pour liberally on any rash of invaders! Elves complaining about your deforestation? Melt the protesters! Your fortress flooding with regular water? Running out of good quality stone to craft with? Pour water and magma together, and you have an obsidian farming operation !
 * In the later versions, there is a magma sea (if you dig to it), magma pools (sort of like magma pipes, with surface in a cave and obsidian coating, and may be linked to the same magma sea) and volcanoes (rare, of course).
 * Now that there are mine carts, a minecart of magma-safe material makes magma handling almost too easy and pump stacks are no longer necessary, except for overkill amount of liquid. Since nickel is as cheap as copper, usually it's possible to bring a magma-safe cart on embark, along with nickel chain for a roller (mechanism can be made from local magma-safe rock). Roller mentioned above is not necessary, but desirable to power the suddenly-heavy cart scooping magma by submersion in a channel — which is less dangerous than pouring it from above or in/out of a lock, since those ways involve a place your dorfs may treat as safe right until it floods with magma, but if a hole is full of magma constantly, dorfs at least aren't dumb enough to go swim there.
 * In Okami, Queen Himiko's palace has a huge pit of lava in it. Oh, and did I mention that said pit of lava is on the second floor of a building that looks easily burnable?!
 * There's also some rather impressive (and considerably more justifiable) lava pits on Oni Island. In both cases, Ammy can swim in them like they're water by equipping an item called the Fire Tablet. She can even use the Waterspout technique on it!
 * World of Warcraft is in love with lava—and Convection, Schmonvection, as evidenced by the abundance of lava pits in zones like Blackrock Mountain, Burning Steppes, Dragonblight, Shadowmoon Valley, Ironforge, and others. It's also not entirely consistent regarding which lava is harmful - there are places where it's almost instantly fatal, places where it's annoying but not a major hazard as long as you get out quickly, and places where you can swim in or walk on it without any apparent ill effects. There's even one zone where you can fish in lava, although what you get out of it isn't edible.
 * You can fish in any lava, with a normal fishing pole. And the perfectly normal fish you catch are not even deep fried.
 * Level up! has lava pits like this and hangs a lampshade on it. If you are badass enough, you can walk it in unharmed.
 * Long, long ago, pre-Halo, the Bungie company had the Marathon series. A few levels take place undeground on some planet, and you can fall in lava if you're not careful. It's like water, except instead of the screen having a blue filter it has a red filter, and your health slides down—quickly, but not instantly.
 * The Elder Scrolls IV: Oblivion has plenty of lava in Mehrunes Dagon's realm (it's treated like water, only you constantly take large amounts of damage from it). Some of the caverns in his realm also have holes in the floor which drop you into pools that have no way out.
 * In The Elder Scrolls III: Morrowind, you can get yourself a lava pit of your own if you become a Telvanni Master and build the tower of Tel Uvirith.
 * In the Awakenings expansion of Dragon Age: Origins, you can find a prisoner suspended in a metal cage above a lava pit. (Convection, Schmonvection, it seems.) You can set him free in exchange for a magical rune … or just be a dick and kick open the cage, sending him plummeting into the lava.
 * Lava pits appear in Sector 4 of Jumper Three. Earlier games substituted floating fireballs for that.
 * World 1 and 4 fortresses in Purple contain lava pits with Podoboo-like fireballs to boot. World 2 fortress has Acid Pools instead.
 * Arachnia in Bug!! has them all over the place. Don't fall in- Mercy Invincibility will not save Bug from becoming ashes!
 * The reason you shouldn't dig directly down in Minecraft.
 * Found in deep depths of Terraria. Also made by players in order to create a barrier or trap for enemies.
 * Daikatana features lava prominently throughout the third episode. While falling in is pretty much certain death in the PC version, the Game Boy version has the character melt into the lava...only to reappear on a nearby platform with only a few health points knocked off.

Western Animation

 * The Predacons in Beast Wars had a lava pit in their base, which  fell into. Also notable was when
 * Several of these are in Miseryville in Jimmy Two-Shoes. They vary between being like water to the people to causing lasting damage.
 * Batman: The Animated Series : The Joker dumps Batman into a trash incinerator in one episode. In another, Red Claw tries dropping him into actual lava.
 * In a variation, the Lava Pit that  in Justice League was an underwater volcano.
 * Apokolips is a world teeming with Fire Pits, which in the finale are implied to be made by drilling right into the planets magma core and letting all the smoke and flame spill out, which gives your atmosphere that nice Fire and Brimstone Hell look. The "implied" part comes when, during their latest Alien Invasion, Apokolips tries to perform this terraforming feat on Earth, turning us into a twisted mirror image of that world purely For the Evulz.

Real Life

 * Most volcanic vents that erupt fluid pāhoehoe lava are fountains, not pools. Lava can pool in depressions downhill from eruption, but they cool rapidly into slower-flowing semi-solid ʻaʻā lava. Persistent actively-convecting lava lakes are extremely rare, and as of this writing there are only five in the world: Erta Ale (Ethiopia), Mount Erebus (Ross Island, Antarctica), Kīlauea (Hawaiʻi), Nyiragongo (Democratic Republic of Congo) and Marum (Ambrym, Vanuatu).
 * THE FLOOR IS MADE OF LAVA!
 * A Steel Mill. Except that it isn't lava but molten metal, and it is far hotter than lava.