Many games provide secret levels that [[UnlockableContent aren't necessary to finish the game.]] Sometimes they are based around [[GimmickLevel gimmicks]] or themes that aren't in the "actual" game. Sometimes they are [[BrutalBonusLevel much more difficult than the main game's and are essentially a secret challenge]], or they feel like they could fit right in the game but the devs couldn't find an exact place to put them in the normal progression (and making them secret was better than leaving them out or [[DummiedOut dummying them]]). Will also be necessary for OneHundredPercentCompletion.

The reward for finishing a Secret Level can range from a [[VideoGameRewards helpful item]], a [[WarpZone shortcut]], some information regarding the story, a full-blown revelation that [[TheEndingChangesEverything changes how the plot is interpreted]], or a pat on the back.

See MinusWorld for such levels that only exist due to glitches.
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!!Examples:

[[foldercontrol]]

[[folder: Action Adventure ]]

* In ''ZeldaIITheAdventureOfLink'', you can go to Darunia and climb on top of houses. If you go to a roof nearest the top of the screen, you can jump off-screen with the JUMP spell, then (while still off-screen) use the FAIRY spell and fly up. You'll get the animation for falling down a hole and end up in a DIFFERENT town. The villagers all provide game info not found anywhere else in the normal towns. If you exit under the overpass to the right, you'll end up in the middle of the ocean, not being able to move in any direction. If you exit to the left, you'll just end up outside Darunia.
* ''Franchise/TombRaider 3'' has a secret level accessed by finding every (well, technically, all but one, due to an oversight) secret. It appears to have been intended to be a normal level (and showed up in various previews of the game) at first but was cut for some sort of progression reason.
** The ''Franchise/TombRaider 2'' GaidenGame Golden mask also has a (very wacky) secret level accessed by finding all the secrets in the previous levels.
*** ''VideoGame/TombRaiderAnniversary'' has the "style units" gained after finding most of the secrets. Not really a level, as it is just an explorable visual demonstration, but it shows off various experimentations with the art-style of the game and locations.
* ''VideoGame/BubbleBobble'', NES (and thus Virtual Console) version has a secret path that the players must take to get the best ending. [[NintendoHard It wasn't there in the arcades]].

[[/folder]]

[[folder: Action Game ]]

* ''RollingThunder 3'' for the Genesis has Rounds A-C (one of them being a NostalgiaLevel) that serves to substitute the two vehicle stages (Round 3 and 6), as well as the Hijack stage (Round 9), while keeping all of their current weapons and ammo.
* ''SyphonFilter: The Omega Strain'''s secret missions are unlocked by completing each block of missions within par time with all of the objectives accomplished.

[[/folder]]

[[folder: First Person Shooter ]]

* Pretty much every early 2.5D FPS (and 3D, with ''VideoGame/{{Quake}}'') has a secret level at some point or other, whether it's once an episode or just one or two in the whole game. They are usually accessed by using a hidden, secret exit on a level rather than the regular exit.
** ''{{VideoGame/Doom}} II'' had two secret levels set in levels taken from ''{{VideoGame/Wolfenstein 3D}}'', with one accessed from a secret exit found in the other. The second one required you to kill four clones [[spoiler:of VideoGame/CommanderKeen hanging from a noose]] to access the exit.
** ''{{Descent}}'' had some secret levels late in the game. They were difficult, but you could be rewarded with a lot of points and some weapons upgrades.
** ''Quake 2'' had three secret levels. The first - Lost Station - has noticeably more enemies than usual, but doing it will reward the player with an early Super Shotgun. The second - Sudden Death - is an interesting one: upon entering, you have 30 seconds to grab as much stuff as you can, then you're thrown back to the previous level and can't enter again. Oh, and its entrance is an innocuous waterfall in plain sight but can only accessed via a RocketJump. The third - Comm Satellite - is [[ThatOneLevel set on a space station accessible via a hidden teleporter and as such, has low gravity and only flying enemies]].
** ''VideoGame/Wolfenstein3D'' itself had a secret level in a gigantic maze where you collect bonus orbs for high score where you're beset upon by four ghosts. Four giant colourful ghosts. With googly eyes. Yes. It's a level of PacMan.
* The Aztec and Egyptian levels in ''VideoGame/GoldenEye1997''. The former deals with the Drax Corporation from ''Film/{{Moonraker}}'', and the latter has [[Film/LiveAndLetDie Baron Samedi]], who somehow procured the [[Film/TheManWithTheGoldenGun Golden Gun]] and is taunting MI6 with it (that level doesn't make a whole lot of sense story-wise, come to think about it). The levels carry their own unique challenges: the Drax soldiers have an over-reliance on grenades which sharp-shooting players can turn against them, and the Egyptian tomb has a GuideDangIt method of getting the Golden Gun.
* The "Panzerknacker Unleashed" missions in ''MedalOfHonor Underground''. They are based on multiplayer maps from the previous game, and they are [[NintendoHard very, very hard]].
* Level 4-0 in ''MedalOfHonor: Allied Assault'' is accessible only through the console, and looks like it was supposed to be part of Mission 3, but was DummiedOut for progression/pacing reasons. There's also the Bazooka-Med bonus level accessed by earning the medal on Sniper's Last Stand.
* The ''VideoGame/{{Blood}}'' GameMod ''Death Wish for Blood'', which places great emphasis on [[DirectContinuousLevels making level transitions logical]], puts a spin on this -- each secret level is followed by revisiting a fragment of the previous map, where the player has to face a single tough fight (usually a boss and his flunkies) before he can head to the regular exit to resume normal level progression.
* The secret levels in ''PerfectDark'' are markedly different from those in ''[[VideoGame/GoldenEye1997 Goldeneye]]'' mentioned above. Instead of brand-new levels with no plot significance, they're retreads of previous levels from a different point of view, which reveal different parts of the story. The first one shows how an alien {{Mook}} [[spoiler:kidnapped the CEO of dataDyne (she was later killed aboard the ship) and imploded the building, effectively destroying the company]]. The other two missions let you play as the [[TheGreys grey]] aliens, one where Elvis alerts the Institute of being captured by Area51 and you play through the entire level with diminished health, and the other has you play as a soldier among a platoon who landed on the planet after Joanna dropped the shields. Both missions are ''[[BrutalBonusLevel insanely]]'' difficult.
* ''VideoGame/{{Marathon}} Infinity: Blood Tides of Lh'owon'' has several of these, which are either alternate endings where the W'rkncacnter destroy the universe, or "co-op carnage break" levels that can (or are supposed to) only be accessed in multiplayer mode. Then there's the three Vidmaster's Challenge levels, found via a secret exit on the final stage.
** The best-hidden secret level is [[http://marathon.bungie.org/story/hangar96.html "Hats off to Eight Nineteen,"]] which can only be reached by noting down strings of hex code found on terminals in the first and last levels, copying them into a text file and unzipping the file twice, whereupon it turns into a map file you can load in the game.
* ''{{Nitemare 3D}}'' goes straight from level 4 to level 6 if you play it normally. Or, you can simply push a bunch of boxes in front of one of a pair of dumbwaiters (which will otherwise just transport you back and forth) and get in the other to jump to level 5, which is full of gun-wielding human enemies.

[[/folder]]

[[folder: Hack And Slash ]]

* The secret Cow Level in ''VideoGame/{{Diablo}}'' 2, which was made after various rumours about one in the original Diablo.
* ''VideoGame/DiabloIII'' has [[SugarApocalypse Whimsyshire]], a land that seems ripped straight from CareBears with smiling clouds, purple bears and unicorns. It can only be accessesd by completing a recipe, or killing a Rainbow Goblin. A later patch also added Greed's Domain, which is a rare portal that opens after killing Treasure Goblins. It features a unique boss and has pots that literally drop millions of gold pieces. Being lucky enough to enter one pretty much ensures you'll never have to worry about money ever again.

[[/folder]]

[[folder: Pinball ]]

* Entering a cheat code in ''VideoGame/LastGladiator'' gives access to a secret "Victors" table.

[[/folder]]

[[folder: Platform Game ]]

* ''RatchetAndClank'' (in ''2'', ''3'', and ''A Crack in Time'') has the Insomniac Museum, where the game's designers stuck a bunch of stuff that "didn't quite make it into the finished game." The handheld entries have the High Impact Games Treehouse, with much the same purpose.
* ''VideoGame/CommanderKeen Episode I'' had a secret level which could only be accessed by going down a tricky side passage in another level.
** Episode four had one where you [[JustForPun collect 12 Inch Worms to make a giant foot]] which then launches you to a secret temple.
* ''SonicCD'' has the DummiedOut 8th Special Stage. To access it, the player has to enter a code in the title screen to open the secret SoundTest, then enter another code on it.
* ''Legend of Grey Moon'' has a number of well-hidden secret rooms; these are typically much easier than the rooms that make up normal areas, if not totally harmless, and most of the time are either silly jokes or completely meaningless. Particularly interesting are one level made of EpilepticFlashingLights which is reached through a secret passage in ''another'' secret room, another containing a secret seventeenth gem, and the Special Thanks To room, a DevelopersRoom of sorts.
* ''VideoGame/WarioLand''; almost every game in the series has many secret levels, including whole secret worlds.
* ''[[SuperMarioBros Super Mario World]]'' also has many, many secret levels and two entire secret worlds.
** ''Super Mario 64'' has various secret levels hidden in the hub area.
** ''Super Mario World 2'' (''YoshisIsland'') had one secret level per world (accessed by 100% completion of the normal levels), generally based around a gimmick, much harder than other levels, or both. The Game Boy Advance remake has another secret level per world once the game has been beaten.
** ''NewSuperMarioBros'' has secret exits that have red flags instead of the standard black flags. Some [[SequenceBreaking let you skip sizable chunks of the game]].
*** Worlds 4 and 7 are also secret worlds.
** ''[[VideoGame/LuigisMansion Luigi's Mansion]]'' has multiple hidden, secret or otherwise unneeded rooms inside the game, which are essential for 100% completion and getting all of the ghosts, but is often entirely optional and one may even forget to do them while playing because those rooms are never mentioned.
** ''[[VideoGame/SuperMarioBrosTheLostLevels Super Mario Bros.: The Lost Levels]]'' has World 9, which the player could access only by playing the first eight worlds without warping.
*** And Worlds A through D, which in the original FDS version the player accessed by playing through the main game [[NewGamePlus eight times]]. In the ''All Stars'' version, you go straight to them after World 8 or 9.
** ''SuperMarioLand2SixGoldenCoins'' has two secret levels in the Pumpkin Zone, and one each in the Tree Zone, Macro Zone, Space Zone and Turtle Zone.
* In both ''VideoGame/SuperMarioGalaxy'' and ''VideoGame/SuperMarioGalaxy2'', Hungry Lumas take Mario and Luigi to secret galaxies after they're fed with enough Star Bits.
* ''VideoGame/DonkeyKongCountry 2'' and ''3'' have a "secret" world that allows access to a better ending, and certain items you collect are focused around gaining access to these levels.
* ''Franchise/CrashBandicoot'' has several of these:
** [[Videogame/CrashBandicoot1996 The first game]] contained to two levels that you needed you to get keys from the Cortex Bonus stages.
** ''Videogame/CrashBandicoot2CortexStrikesBack'' has levels hidden within levels. Some of these are considered parts of the main level [[GuideDangIt where you really need to know what you're doing]] to find them...
*** ... For instance, there's the hidden area within the Unbearable level, where you need to [[LeapOfFaith jump into a seemingly bottomless pit]] in order to gain access to a hidden area within the level, which swaps the level theme from a towards the screen chase sequence to a side scrolling section.
*** ...On another level, the player has to jump on what looks like a conspicuously static stack of Nitro crates to teleport to a secret section and get the purple gem.
*** ... Then there are the levels which you need to unlock by finding secret bonuses in other levels, such as standing on a hard to get to platform, or jumping over a long [[BottomlessPit hole]] to get back to the polar bear, in order to unlock hidden levels, and alternate paths in other levels.
** ''Videogame/CrashBandicoot3Warped'' does the same once again in accessing hidden levels with alternate routes, but makes you beat time trials to get to them. However, there are still two hidden levels not at all required for 100% completion, but required for 105% completion. While all of the secret levels in ''Crash 2'' can be found without a guide with enough persistence, ''Crash 3'''s secret levels are really obscure. One of them has you driving into a sign on the side of the road in a motorcycle level.
* ''[[VideoGame/Sonic3AndKnuckles Sonic and Knuckles]]'' had both secret areas that were only accessible by one of the characters, and a different final stage for HundredPercentCompletion.
* ''VideoGame/{{Iji}}'' has Deep Sector, featuring a fun little battle against ''seven'' Assassins. Considering the most you ever have to deal with at one time other than that is ''one''....
* ''{{Eversion}}'''s secret level is unlocked after collecting all 240 gems in the game, and is necessary to get the good ending.
* ''DemonsCrest'' really has no mandatory levels after the very first stage, but the final two need to be unlocked on the world map by jumping into a cyclone in Stage 4.
* ''[[VideoGame/MeatBoy Super Meat Boy]]'' has regular secret levels which qualify as bonuses (required for HundredPercentCompletion), and then has intentional "''MinusWorld''" levels, which are just plain [[NintendoHard sadistic.]]
* In ''VideoGame/MegaManX3'', there's a secret level that can only be accessed through specific teleportation capsules, that take you to an abandoned factory where you can fight Vile, TheDragon of the first game. Finding and beating him will result in another boss appearing in his stead later on, where he would normally find and attack you.
** Then, in ''VideoGame/MegaManX6'', there's a secret "Nightmare Stage" for every normal level, where you can find secret upgrades and bosses.
* ''VideoGame/RollAway'' has two kinds of secret level; trippy Bonus levels reached upon collecting five friuts where you have to hit every block, and regular levels [[RecycledInSpace IN SPACE]] reached from secret exits.
* World 8, [[BubblyClouds Sky Roost]] in ''[[Videogame/HarmoKnight HarmoKnight]]'', which is unlocked after collecting 5 Tori Birds, is an entire Secret Level merged into one big world. It tries to mimick the earlier worlds, but (as the princess says) puts a twist on them. These eight levels look like normal levels, but then you enter one of the levels, and see thousands of Mooks, SpikesOfDoom, and BottomlessPits. You get the sudden realization that the princess told you these levels are NintendoHard. Final Trial is just simply [[DeathCourse a gigantic death trap]].
* ''KidChameleon'' has many levels named "Elsewhere". All of them are technically secret levels. Early on, they generally have to be discovered and act as shortcuts, but later in the game, there are plenty that can accidentally be accessed and lead backwards (or just through to a different path of levels).

[[/folder]]

[[folder: Puzzle Game ]]

* ''VideoGame/{{Gruntz}}'':
** Each level has areas accessible only with the use of red wormholes (which appear temporarily if you step onto a specific tile) and secret switches (which make parts of the terrain change temporarily).
** Additionally, it seems that the game was intended to also have actual secret levels. They would be unlocked if a grunt carrying a specific tool (most likely one that is impossible to get on the main level without cheats) steps on a specific tile. However, only one such level made it into the game.

[[/folder]]

[[folder: Real Time Strategy ]]

* ''{{Starcraft}}: Brood Wars'' featured a secret mission which hinted at a major plot point in the sequel. It had no lasting impact on the game otherwise. Said sequel also features a hidden mission in the Terran campaign.
* Similarly, ''{{Warcraft}} 3: The Frozen Throne'' had a hidden tower defense mini-game. If you defeated all the waves, you would receive a bonus hero in the following level.

[[/folder]]

[[folder: Role Playing Game ]]

* ''{{Quest 64}}'' has a SecretLevel in the [[ShiftingSandLand desert]]. While in a completely unrelated and skippable area, it does have a ton of powerups which are normally hard to find.
* ''DarkSouls'' has The Painted World of Ariamas, the Great Hollow, and the Ash Lake. For the most part, they're difficult-to-find [[BreatherLevel Breather Levels]] with lots of really good loot.

[[/folder]]

[[folder: Stealth Based Game ]]

* "Requiem," the final mission of ''VideoGame/{{Hitman}}: Blood Money''. When it starts, it appears to just be a screenshot of 47's funeral over which the end credits are actually playing. Twirling the analog sticks (or pressing "W" on the computer) eventually causes 47 to get up, at which point the credits disappear and the mission begins. (This level is so secret that, on the Xbox versions, an achievement is awarded for completing the game after finishing ''the previous level''. Realizing that there ''is'' a mission in "Requiem," and then completing it, is good for a second achievement of equal value.)
* ''VideoGame/SheepDogNWolf'' has two, both cleverly hidden in the HubLevel. One at the end of a passage in a wall that looks like a completely ordinary wall, and the other accessed by entering one of the doors from the other side.

[[/folder]]

[[folder: Shoot Em Up ]]

* The SharpX68000 port of ''FantasyZone'' has a secret eighth stage, "Dragon Land," based on ''VideoGame/SpaceHarrier''.
* ''{{Rez}}'' has the Lost Area, unlocked by completing all the normal areas. [[BrutalBonusLevel It is quite difficult]]. Same for ''ChildOfEden'''s Hope level.
* The original ''StarFox'' has the Black Hole and Out Of This Dimension, both accessible from the two Asteroid Belt stages.
* ''VideoGame/{{Tyrian}}'' is absolutely chock-full of secret levels. As a rule, they're accessed by destroying a specific target in a level so that a big glowy sphere appears. When you grab it, you'll move on to the corresponding secret level after finishing the current one. Some of these are tough to get, requiring you to leave certain enemies alone or stay on a certain path. There's even secrets 'within' secret levels, so you can go through a bunch of secret levels in a row before returning to the normal ones.
* ''VideoGame/{{Gradius}}'', as a series, is flat-out obsessed with hidden levels. Most games in the series have a secret alternate path, usually be doing something during the level to change the boss you fight. This gets lampshaded in ''[=ReBirth=]'', where you can fight a different boss but end up in the same level 2 stage regardless - the actual Secret Levels (there are three) are much better hidden. Not every game uses hidden stages, but rather Multiple Paths.
** The self parody series ''VideoGame/{{Parodius}}'' makes fun of this along with everything else - the secret levels in some of those games are even more insane than the standard ones.

[[/folder]]

[[folder: Wide Open Sandbox ]]

* ''SaintsRow2'' has ''Revelation'', which provides closure to the ending of [[SaintsRow1 the first game]] and is not unlocked through the standard story progression. Instead, you are given a hint to go to the police headquarters, where you can listen to three wiretap conversations and find Dex's phone number, who directs you to the mission start.
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