''The Thirteenth Floor'' is a 1999 science-fiction crime thriller based on the 1964 novel ''Simulacron-3'' (also known as ''Counterfeit World''), by Daniel F. Galouye.

For years, Douglas Hall has been working with his friend and mentor, Hannon Fuller, to create a simulated world. Not merely a computer game, their simulation is a SmallSecludedWorld where the inhabitants don't know that they are simulated. They believe that their world is the real world of 1937, not just a simulation in a cluster of supercomputers at [[TitleDrop the thirteenth floor]] of some future skyscraper.

Now someone or something has murdered Fuller, and seem to be trying to pin the blame on Hall. The answer to the mystery is somewhere in the world they created together... But their world is not safe anymore. Simulated humans are awakening to the terrible truth of their existence, wanting revenge on their deceitful creators.
!!This film provides examples of:

* AnachronismStew: Fuller's alter ego mentions having been "in World War One". Nobody would have numbered it in 1937, before the second had ever happened. It's probably intentional, as this 1937 is not a 100% real representation of how it was, but is a "recreation of 1937 from (Fuller's) youth." The programs are following what they've been programmed to, which would include mistakenly call the first world war "World War One" because they're created by post-WWII programmers.
* AndTheAdventureContinues: [[spoiler:It's implied at the ending that what they consider to be the real world is actually yet another simulation.]]
* BaitAndSwitchGunshot: [[spoiler:Jane Fuller is running away from David), and finds herself in a wide open space with nowhere to go. David lifts his gun and she closes her eyes, ready for the worst. The camera stays on her, there is a bang and she shudders but a second later she opens her eyes, and we see that her husband has been shot by Detective [=McBain=] instead]].
* CityInABottle: Inside a computer system [[spoiler:[[{{Recursion}} inside a computer system]]]] possibly [[spoiler:inside a computer system]].
* ColorWash: Douglas Hall comments on the colors being "off" in the simulated world.
* {{Cyberspace}}: Kinda.
* DeadpanSnarker: [=McBain=]
* DramaticThunder: Rolls during the climactic BaitAndSwitchGunshot scene.
* {{Foreshadowing}}: "The colorization's a little off, but none of the units seem to notice."
* TheFutureIsNoir: As is the present, and the past. It's safe to say that this is one of the noir-iest movies ever made.
* GainaxEnding: [[spoiler:Right before the credits, the scene is "switched off" with a CRT-like effect. Just a fancy animation, or a heavy hint that the "real real world" is actually another simulation? The ending is open to the viewer's interpretation.]]
* AGlitchInTheMatrix: The boundary of the simulation is located at the end of a long road, where the rendering of the simulation just fades into wire-frame and its sounds become very artificial.
* GoMadFromTheRevelation:
** Happens when Ashton, a bartender from the 1937 simulation, finds a letter that leads him to suspect his world is not real. He goes homicidal when he encounters one of the creators of the simulation.
** [[spoiler: Douglas]] has a minor breakdown when he discovers "the End of the World".
* HeroicBlueScreenOfDeath: [[spoiler: Douglas Hall]] upon learning the truth.
--> '''[[spoiler: Douglas]]''': Yeah, there's just one little flaw in your thesis. ''None of this is real!'' You pull the plug... I disappear! And nothing I ever ''say'', nothing I ever ''do'', will ever matter!
* HydePlaysJekyll: [[spoiler:The main character Douglas Hall was taken over by David, a "user", who then pretended to be Douglas.]]
* IgnorantOfTheirOwnIgnorance: Ashton starts out like this, but is brutally awakened to the true nature of reality.
* InsideAComputerSystem: Much of the plot takes place in the 1937 world. [[spoiler:The "real world" is also a computer simulation. Eventually the hero gets uploaded to "the real real world" unless that world is ''also'' a computer simulation.]]
* IWantMyJetpack: [[spoiler: Douglas Hall discovers he's really in a VR simulation of the 90s created in 2024. At the ending he gets to see what 2024 looks like, and the buildings are all bizarre "futuristic" things out of Buck Rogers.]]
* TheKillerInMe: [[spoiler: Douglas Hall has blackouts during which he is forced to carry out bad deeds.]]
* KissMeIAmVirtual: Fuller turns out to have been visiting the 1930's so he can have sex with showgirls (he would have been a teenager in the 1930's, so this fetish is understandable). Goes into WhatMeasureIsANonHuman territory because the character he takes over has marital problems when he comes home with no memory and smelling from perfume.
* LawOfConservationOfDetail: In-film. Suspecting you're in a simulation? All you have to do is [[ScriptBreaking go somewhere the simulation doesn't assume you'd reasonably want to go]]. The places you live in are all rendered completely to avoid such accidents happening by chance, but animating and rendering the world way beyond what you're expected to experience is pointless and expensive. So the farther you go, the less alive and moving the world becomes, until the simulation gives up entirely and shows an almost detail-free wireframe scenery.
* LoveAtFirstSight: Played with. Hall and Jane Fuller meet and are immediately attracted to each other; after a brief dance they reflect on the fact that both seem to be already familiar with each other, and the girl says deja-vu is usually a sign of love at first sight - and sure enough, they fall madly in love. [[spoiler:It later turns out the girl has been watching him from the start of the simulation, and has been in love with him for a long time; he, instead, has been modeled on the girl's husband, and has had regular memory interference from him - hence the familiarity.]]
* RecursiveReality: Worlds within worlds.
* SchrodingersButterfly: What is real and what is the simulation?
* WhatHappenedToTheMouse: Grierson, loyal husband and very innocent in all the mess, is - from his perspective - [[spoiler:unceremoniously dumped at the table by the person who got him there, who then never returns. So Grierson is left in the middle of the place where his alter ego used to go to have sex with the girls and everyone knows him and what "he" does, but he doesn't know anyone - though he has faint memories of what his alter ego used to do.]] And while Hall is busy doing his things, the poor guy must be feeling like he's losing his mind.
* WorldLimitedToThePlot: Deconstructed, as this plot is actually about writing reality itself.
* YourMindMakesItReal: You enter a virtual world by possessing one of its inhabitants and if killed in this state, ''your'' mind dies. And not only that, but [[spoiler: the victim's mind takes over your body instead because it turns out the process is actually a complete mind swap. No one realized this because the real body usually remained completely unconscious during the process. Virtual death merely broke the connection and jarred the real world body with the virtual mind inside it awake.]]