Big Labyrinthine Building

This building is so big and labyrinthine that few people know its deeper recesses. It might or might not contain big rooms or pieces of equipment, but a lot of the bulk is taken up by ordinary-sized rooms and corridors. Overlaps a lot with Building of Adventure. Compare Clown Car Base.

Mobile Maze is possible.

Big Fancy Castle is a subtrope with medieval look-and-feel.

Anime

 * In Macross/Robotech, Rick and Minmay actually get lost inside the SDF-1 (a Giant Robot big enough to fit a small city inside) for an episode or so. Later a party of humans find themselves hiding in an immense forgotten corridor on a Zentraedi ship that's even larger than the SDF-1. In the second season of Robotech, the alien invaders' colony ships are similarly vast.
 * Library Island of Mahou Sensei Negima. It's basically a dungeon straight from a video game. There is an entire school club devoted to exploring it, who use rock climbing gear. And its still a functional library. Behind every waterfall, in the deepest of pits and tops of towers, down every winding and mazelike corridor, even in the crawlspaces, lie shelf after shelf of books. Books that take no damage from being behind waterfalls.
 * In the Negima!? anime series by Studio Shaft, the waterfalls are made of books too! There's even an apparent replica of New York City complete with a statue of liberty, all made out of books.
 * Las Noches from Bleach has some high ceilings and a county-sized opening in the center, but even without these, it's still roughly the size of a small country.

Comics

 * The Infinity Avengers Mansion from The Avengers, created by Hank Pym during Dan Slott's ongoing run. The Mansion exists in a quantum state in between dimensions, and it is, well... Infinite.
 * The Keyhouse Mansion from Locke & Key. The Magical keys found inside it are the main theme of the series, and all of the Keyhouse's secret have not been revealed yet.
 * The Rich family mansion in the Richie Rich comic books is large enough that its roof once served as an emergency runway for an airplane! The Rich Manor map has 2/3 of it labelled simply as "unexplored sections of the mansion".

Film

 * The Cube
 * House on Haunted Hill
 * Dr. Frankenfurter's castle in The Rocky Horror Picture Show

Live Action TV

 * The TARDIS from Doctor Who. In one episode, the Doctor, looking for a remote room, leaves thread behind him so he can find his way back.
 * In Battlestar Galactica Reimagined, there is a forgotten astrogation room on board the Galactica that was abandoned when the design for the Galactica's navigation system was changed.
 * In Star Trek, the Jeffries tube passageways. In one Star Trek: The Next Generation episode, the crew heard music coming from where it shouldn't. It was Captain Picard playing an alien flute in a Jeffries tube; he liked the acoustics there.
 * The Centre on The Pretender

Literature

 * The House of Leaves is a house that is bigger on the inside and contains odd angles and possibly other things. When asked to draw it, a kid produced an all-black drawing.
 * The Mirror of Her Dreams gives us Orison, a castle full of Bizarrchitecture.
 * Hogwarts, from the Harry Potter books.
 * The Tower of the Egg in Robert Heinlein's Glory Road.
 * Gormenghast
 * Also the palace in Michael Moorcock's Gloriana (Moorcock being a huge Peake fan).
 * The Labyrinth in Robert Silverberg's Majipoor series. Home of the Pontifex, who is always the last Coronal to serve on Castle Mount. This strange city is in a desert region and is built almost entirely below ground. Many layers beneath the ground, the bureaucracy that actually runs Majipoor is busy with their statistical analyses and other "official" paperwork. The Pontifex himself, technically the top executive of the planet, is more or less stuck here.
 * The hospital in Connie Willis' Passage is like this, complete with bizarrely-connected buildings and elevators leading to many instances of "you can't get there from here", work crews randomly blocking passages, forgotten stairwells where the paint dried long ago and a never-open cafeteria. This is pretty relevant in a book where everybody keeps missing each other, hiding from each other and being chronically late, so much so that when at the end the doctor arrives in time to save the Littlest Cancer Patient it's a Crowning Moment of Awesome.
 * Unseen University from the Discworld, though technically a complex rather than a building. It is noted that due to the high magic levels in the University and low amounts of reality in the Discworld 'verse, UU is constantly adding and subtracting rooms on a daily basis. A map of the place looks like a chrysanthemum in the process of exploding, and is only anywhere close to helpful for maybe a week at best.
 * This especially applies to the library, as large numbers of books disort time and space around them. In one book it is claimed that every used book store in existence belongs to this trope, and that their owners have actually gotten lost from other dimensions where erratic opening hours are a respected form of business.
 * There are several examples in Jorge Luis Borges's works, most notably the City of Immortals (The Immortal), which is a whole city built like this.
 * The Book of the New Sun has the House Absolute - the home of the Autarch. Not only is the House so vast and complex that its extents are unknown, but there is a secret "Second House" coextensive with the first. The Citadel of Nessus is also vast and labyrinthine, but arguably more a complex than a single building.
 * Willy Wonka's chocolate factory, in Charlie and the Chocolate Factory.
 * The Ursula K. Le Guin short story "The Building" from the collection Changing Planes centres around a race of people who once a year travel an enormous distance to continue work on a gigantic, labyrinthine, never-to-be finished building for no purpose anyone (including the builders themselves) can discern.
 * The White Council Headquarters in Edinborough in The Dresden Files.
 * The Palace in Septimus Heap is described as such.

Mythology

 * The Ur Example is the palace of King Minos, in Knossos. It was the basis for the myth of the Labyrinth built by Daedalus to imprison the Minotaur.

Real Life

 * The Pentagon.
 * Allegedly: the pyramids. In actuality most of their volume is cut stone / cement, but it is certainly plausible that undiscovered passageways exist.
 * Several have been discovered by modern technology, but left unopened. Some most likely played part in the construction process, while others may have religious significance, or burial chambers. They are largely unconnected to each other, and isolated from the main tunnels by tons of stone, making potential excavation tricky business.
 * The Gunkanjima Island in Japan. It tops on a coal mine; the area of the island is 15 acres, and its built-up area is 16 acres - meaning that the whole island is one continuous humongous maze of buildings - extending at some places over the sea.
 * The Winchester Mystery House (scroll down to #4). A house in San Jose, with 160 rooms, built like a maze to confuse ghosts - with stairways disappearing into the ceiling, doors opening into walls, and lots of 13's strewn about the place.
 * The British houses of parliament have more corridors in meters than the White House has floor space in square meters.
 * The British Prime Minister's office at Number 10, Downing Street also applies to this trope, since the apparently relatively modest-sized upper-class house has been expanded to all the neighbouring buildings while retaining their original fronts intact.
 * According to Jeremy Clarkson, the BBC Television building is one of these.
 * Any Steel Mill. The MMK integrated mill in Magnitogorsk, Russia, is a riverside of eleven kilometres of continuous buildings, furnaces, workshops, corridors and halls.
 * Likewise, paper and cellulose mills qualify as big labyrinthine buildings.
 * Many large hospitals qualify, as they're generally expanded as funding allows, and it's easier to get most donors and foundations to pay for a new wing than a separate building. It's not just some patients' lack of mobility that makes it necessary for orderlies to transport them around the place in wheelchairs: it's to keep them from getting lost on their way to Radiology.
 * Shopping districts in colder cities are often interlinked by skyways and underground corridors so customers can move freely while avoiding the weather, essentially merging them into this trope.
 * Colleges are rife with Big Labyrinthine Buildings; varying ages of buildings, additions, flirtations with experimental architecture, large buildings built on hills (so that there are short stairs, confusion as to what floor any given floor is, and sometimes the impossibility of using a single stairwell or elevator to get from the bottom to the top. Good luck if you're disabled.) The tendency of many colleges to have "buildings" that are connected to each other or even full-on contiguous translates into a lot of very confusing buildings. It's probably related to space and funding, as with the hospital example, except college donors prefer to finance buildings.
 * Padelford Hall at the University of Washington, housing the Math, Linguistics, English,Comparative History of Ideas, and Spanish departments, known for being hard to navigate (the third floor of C-wing connects to the second floor of B-wing being one of its more benign quirks). Also, the UW Medical Center, which is.....very, very large....
 * Several buildings of the Budapest University of Technology and Economics, most notably the central "K" building - it's so confusing for new students that there is a map with a route planner on the website. Since the rooms were renumbered recently, it will be confusing for older students too.
 * Large airports, particularly when one massive terminal building is used rather than multiple smaller ones. One example that comes to mind is Miami International (MIA), with all kinds of lengthy passageways used to access remote "headhouse" gates, to accommodate international arrivals, to transfer between flights, and to access ground transportation. It was really a labyrinth while the new North Terminal was under construction. Some airport terminals make use of moving sidewalks, or even peoplemovers to navigate within.
 * Resort hotels, especially the old-school "Borscht-Belt" resorts in New York's Catskill Mountains, such as Grossinger's and the Concord. These places were designed so that guests could walk between one of multiple lodging structures and: the lobby, the dining rooms, the indoor pool, the health spa, the nightclub, the game room, the on-site stores, and the coffee shop (some also had indoor mini-golf and/or a skating rink) -- all without ever stepping outside.

Tabletop RPG

 * Al Amarja's "D'Aubainne International Airport" terminal in Over the Edge.

Video Games

 * The level 'Slumberland' in Glider PRO is a perfectly ordinary 400-room house.
 * Every dungeon in in every The Legend of Zelda game. Its worth mentioning that a decent number of them are temples which really brings up the issue of where the prayer goes on, and why the faithful have to get by lava, bottomless pits, and several false paths to get to it.
 * Offices in City of Heroes go all over the place, with random elevators that service only two floors, small rooms suspended in larger ones that can only be reached by a walkway that in turn can only be reached via a different room, etc.
 * The Temple of Ix from Nox is built like a maze filled with traps, monsters and various confusing hallways. This is because it's designed to keep intruders from taking the Weirdling. Dun Mir and Castle Galava also count.
 * Black Mesa, from Half-Life.
 * The Enrichment Center in Portal and Portal 2.
 * Lampshaded in Tales of Symphonia with regard to the second Renegade base, which Lloyd refers to in a skit as 'big for no reason'.

Web Comics

 * The eponymous Gunnerkrigg Court
 * The Mansion of E
 * Castle Heterodyne of Girl Genius

Western Animation
"Professor Farnsworth: You can't just waltz into the Central Bureaucracy. It's a tangled web of red tape and regulations. I've never been, but a friend of mine went completely mad trying to find the washroom there. Leela: Then we'll need a guide, someone who's been there before. Professor Farnsworth: Oh, I've been there. Lots of times. *Maniacal Laughter*"
 * The Central Bureaucracy in Futurama:


 * Fosters Home for Imaginary Friends; Madame Foster apparently once got lost in its halls for weeks.
 * The Place that sends you Mad from The 12 Tasks of Asterix is set in a Labyrinthine office building. The unhelpful personel only make it worse.
 * In Codename: Kids Next Door, the protagonists' massive Treehouse of Fun towers over the surrounding neighborhood and is full of odd rooms like an aircraft hangar and a "cheese repository." While its absurd size isn't usually a plot point, one episode has the kids trekking through the most of the treehouse to stop a lice infestation, while another establishes that there's a long-abandoned lawless section of it with tribal ginnea pigs.
 * Even better: each sector of the KND has their own massive treehouse that's likely just as labyrinthine!
 * Phineas and Ferb build one, of course.