[[quoteright:350:[[Manga/FullmetalAlchemist http://static.tvtropes.org/pmwiki/pub/images/FMA_gate_of_truth_7086.jpg]]]]
[[caption-width-right:350:Step inside, don't be shy! There's everything you'd ever want to know... ''[[EquivalentExchange for a price.]]'']]

->''"It was like all the information in the world was being poured into my brain at once. My head felt like it was about to burst, but for an instant, it became clear: the truth of everything."''
-->-- '''Edward Elric''', ''Manga/FullmetalAlchemist''

The Gate of Truth is a central nexus of all knowledge in the universe, or something close to that. Tends to be difficult, if not nearly impossible to reach. If the answer is [[Franchise/TheHitchhikersGuideToTheGalaxy Forty-Two]], then chances are, the question is somewhere in there. It may or may not be [[GeniusLoci sentient]], and may or may not be actively collecting knowledge, but what's important is that it already has a lot of it in stock. If it's known at all to people, those who know about it are very likely to be an elite of some sort, and will more likely than not be killing each other just to get there.

{{God}}, or [[EldritchAbomination something]] [[SufficientlyAdvancedAlien like that]] might be guarding it to protect all the secrets within, if they are not the same being as the gate itself. Else, there's probably a [[ThresholdGuardian toll-keeper]] who requests a [[EquivalentExchange small fee]] before you can take a peek at its vast repository. The point is, the knowledge is collected, and a block has been installed that keeps everyone from just wandering up and partaking of it.

Whether or not the knowledge gained was worth the cost depends on which end of the SlidingScaleOfIdealismVersusCynicism the story lies.

Note that the Gate of Truth need not necessarily be a literal gate. It could be a [[TheWorldTree tree]], a [[WesternAnimation/{{Futurama}} scary door]], or even the [[ArsonMurderAndJaywalking corner of Rhodes and Fourth Street]]. "All knowledge" need not be a literal description, either. Simply ''a lot'' will do.

See also MagicalLibrary, OmniscientDatabase, GreatBigBookOfEverything, TomesOfProphecyAndFate. SuperTrope to the AkashicRecords.



[[folder:Anime and Manga]]
* The [[TropeNamer Gate of Truth]] from ''Manga/FullmetalAlchemist''. Truth, [[TheBlank a white, featureless]], {{jerkass|Gods}} [[OurGodsAreDifferent godlike being]] whose physique matches that of the person entering his realm, is the gatekeeper. [[spoiler:You pay with a part of yourself, which Truth then wears until you reclaim it, assuming you ever do; in exchange, you gain the ability to perform alchemy without a transmutation circle.]] At the end, it is revealed that [[spoiler:it is possible to pay with your Gate instead of your body parts; however, this renders the alchemist unable to perform alchemy ever again, and unless he somehow is tied to another person's gate, will strand him in Truth's realm until he dies, [[{{AndIMustScream}} and that's if you die.]]]] This places FMA clearly on the idealist side of things; the knowledge that Edward gained from the Truth didn't really help him all that much; more than that, he started to believe that the knowledge he gained could help him overcome any obstacle, and thus he became Truth's puppet. In the end, [[spoiler:although he loses his ability to perform alchemy, as long as he has his friends, he's happy.]]
** Works slightly differently in [[Anime/FullmetalAlchemist the 2003 anime version]]. There is no gatekeeper; rather, the Gate itself is implied to be sentient. Also, the Gate is, in fact, [[spoiler:a portal between the world of the series and our own world, and thus the source of [[PoweredByAForsakenChild the soul energy that powers Alchemy]]]]. It is inhabited by [[spoiler:weird black imps that do the body part-claiming in Truth's stead -- and for a short period of time, the homunculus Wrath until Ed provides him with a means of escape. It's implied the imps are actually the souls of those who die in our world]].
* ''Anime/{{Mnemosyne}}'' has Yggdrasil actively trying to become this by casting time spores on the world and using them to gather data.
* The Galactic Leyline from ''Manga/OutlawStar'' is mainly one of these, though it also grants wishes. If you can reach its center in one piece.
* The quantum computer from ''[[BattleAngelAlita Gunnm Battle Angel Alita: Last Order]]''. [[spoiler: It uses the collected brains (the collective unconscious of humanity) as a means to predict the future.]] Zalem keeps it a heavily guarded secret from ''everyone''.

[[folder:Comic Books]]
* In ''{{Planetary}}'' there's a supercomputer composed of thousands of souls under the streets of Hong Kong, it chooses a "champion" in the form of a cop killed by their partner as betrayal.
* The Source in the {{DCU}} is close to this trope.

* In ''Literature/TheOdyssey'', there are two gates through which all dreams pass, one of horn and one of ivory. Dreams that pass through the horn gate are true (that is, they come to pass in RealLife), whereas dreams that go through the ivory gate are deceptive and false.
** This particular imagery recurs in ''Literature/TheAeneid'' and in many later works. English-language works making use of the motif include ''Literature/TheFaerieQueene'', ''Literature/AWizardOfEarthsea'', Robert Holdstock's fantasy novel ''Gate of Ivory, Gate of Horn'', and ''ComicBook/TheSandman'' by NeilGaiman.
* In Creator/NeilGaiman's ''Literature/{{Neverwhere}}'', the angel Islington guards, among other things, the door to Heaven, hidden in the deepest part of the London Underground.
* From the CthulhuMythos, Yog-Sothoth is the Gate. Yog-Sothoth is the Key. Yog-Sothoth is the All-In-One and the One-In-All. [[TimeyWimeyBall Past and present are one in Yog-Sothoth.]] He alone knows where the [[EldritchAbomination Great Old Ones]] walked the Earth's fields, and He alone knows where they shall do so again and why none can behold Them when They walk.
* "Deep Thought" from ''Franchise/TheHitchhikersGuideToTheGalaxy''.
* The vignette "A Man Before the Law" in the Creator/FranzKafka novel ''The Trial'' is a [[SubvertedTrope subversion]], in that the man trying to enter the gate that leads to the law itself never gets to enter despite spending an entire lifetime trying to learn the required price.
* Many fictional uses of the RealLife Library of Alexandria, which was lost or destroyed depending on which story you believe, have it become one of these.
* In ''Literature/TheDresdenFiles'', The Archive or "Ivy" is a living example, as she knows everything that has ever been written, and is updated in realtime, to the point that Harry sends her a note using this. Its a bloodline ability, passed from mother to daughter.

[[folder:Live Action TV]]
* In ''Series/DoctorWho''
** Rose Tyler looked into the Heart of the TARDIS and it poured all the information in the universe into her head, turning her into a God-like being called "Bad Wolf".
** Also later in the series, the Doctor describes all the time lords looking into hole of space and time as children and seeing different things, some seeing all the secrets of the universe.

[[folder:Religion and Mythology]]
* Mimir's Well, from NorseMythology. Odin paid for his wisdom with one of his eyes.
* In the Literature/TheBible, God would seem to be this, since he is omniscient - he "knows all". The Bible also has the Tree of Knowledge where Adam and Eve got the ForbiddenFruit.

[[folder:Tabletop Games]]
* The Black Library in ''TabletopGame/{{Warhammer 40000}}'' contains every piece of information about [[TheCorruption Chaos]] ever collected. It exists in an unknown location deep in the Eldar's [[PortalNetwork Webway]], is guarded by the secretive, dangerous Harlequin cult of Eldar warriors, and only a handful of humans (most notably [[GodEmperor the Emperor]]) have ever reached it. Considering that much of the information is ThingsManWasNotMeantToKnow, the security is necessary.

[[folder:Video Games]]
* A.B.A's instant kill attack in ''GuiltyGear'' causes one of these, inscribed with the Kabbalic Tree of Life to appear, open, and suck the enemy in on a successful hit. The door slams shut, and is then locked shut by her giant monstrous key. "Destroyed!" intones the announcer.
* In the lore for Franchise/TheElderScrolls, [[EldritchAbomination Hermaeus Mora's]] plane of Oblivion is an eternal library where all forbidden knowledge can be found.
** The Elder Scrolls themselves are a portable version of this, since they contain the secret to the very fabric of the universe... and if you try to just read one normally, you go temporarily blind.

[[folder:Web Comics]]
* The Seer from ''Webcomic/KidRadd''. Everyone who takes his advice ends up dying in some contrived way, usually [[SelfFulfillingProphecy because they took his advice]].
* The Valley of the Oracle in ''Webcomic/TheOrderOfTheStick'' is a test of prowess and wit for those seeking the Truth, and if they succeed, they can get a True answer to any question. But they can't take the whole truth with them; on leaving, the Memory Charm placed on Sunken Valley wipes their memories of everything except their question and the answer.
** Although Roy accidentally discovers a way to work around the Memory Charm: [[spoiler:as a ghost, he annoys the Oracle enough that he banishes Roy (using a magic item, the Oracle has no actual Divine magic), not realizing that banishing Roy bypasses the Memory Charm.]]

[[folder:Western Animation]]
* ''WesternAnimation/AvatarTheLastAirbender''
** Wan Shi Tong's Spirit Library is this, complete with scary spirit guardian. There's a reason his title is "He Who Knows Ten Thousand Things". He also has fox servants that regularly bring back more knowledge.
** The spirit world itself; Aang has to brave various monstrous terrors so that he can ask questions of his previous incarnations.
* An episode of ''WesternAnimation/JusticeLeague'' features the library of Hades himself, located in [[FireAndBrimstoneHell you-know-where]].
* The [[AmuletOfConcentratedAwesome Matrix of Wisdom]] from ''Franchise/TransformersGeneration1''. When opened, it destroys an intergalactic HatePlague by unleashing its accumulated wisdom.