One of the oldest, but also most underappreciated, Videogame Settings.
In the same way a Mini-Boss can be placed halfway through the way to the whereabouts of a main boss, a mini-dungeon is a location accesible through the overworld that appears as a precedent to a main dungeon. It is explored for a particular purpose, but in terms of storyline it's less important than a main dungeon. Because of the lower importance, the mini-dungeon has a simpler layout and design, and thus it's not too difficult to tackle. Though the standards of the average mini-dungeon can vary according to the game, there are some general characteristics shared by most of them:
As mentioned before, it's less complex and intrincate than main dungeons. As a general rule, it's not guarded by a boss, but rather a mini-boss.
It can share some traits and trends with the dungeon it's preceding, thematically or in terms of gameplay.
It may combine some aspects of a normal overworld area, similar to a Dungeon Town.
In some cases, it's a place that is intended for characters to test their skills before venturing into the more dangerous dungeons.
By nature, almost any Noob Cave is in and of itself a mini-dungeon, unless the first area in the game happens to be of a caliber as high as that of any further level.
From Super Mario Bros. 3 onwards, it has been a tradition in subsequent 2D Mario games to have a midway-placed Fortress level in each world (two in some cases), often guarded by a Mini-Boss that appears recurringly through the game. In the case of Super Mario World, in addition to having fortresses, it also introduced Ghost Houses, and one of them is even guarded by a mini-boss: Big Boo.
By extension, this also applies to the two Yoshi's Island games, though the mini-boss in each fortress is unique to it. There's also "KEEP MOVING!!" in the first game, played right before the final level, that even has the castle/fortress theme heard.
In the fourth episode (game) of Commander Keen, the Castle of Sand Yego is played similarly to the Pyramids (the game's resident dungeons), but it's optional and serves mostly to prepare the player for harder levels.
Most mini-dungeons in The Legend of Zelda are present for Link to search items, abilities or anything else necessary to enter the main dungeons:
Southern Face Shrine in Link's Awakening. It houses the Face Key that gives access to the northern Face Shrine (main dungeon).
Ice Cavern and Bottom of the Well in Ocarina of Time. The former is necessary as Link earns there the Iron Boots, which are required for tackling the Water Temple. In the latter, the Lens of Truth lies within, and is necessary for navigating the Shadow Temple. To a lesser extent, there's the Thieves' Hideout, inside which the young hero has to rescue the four carpenters before he can proceed into the desert.
At least four in Majora's Mask: The Deku Palace where Link infiltrates to learn a song that gives him access to Woodfall Temple, Pirate's Fortress to retrieve the Zora Eggs which are the key to learn the melody that opens the way to the Great Bay Temple, the Gibdo Well to get direct access to another mini-dungeon, the Ancient Castle of Ikana, where in turn Link looks for a way to get access to Stone Tower Temple.
The Bokoblin's fortress in Twilight Princess, immediately preceding the Arbiter's Grounds.
The pyramidal tombs in Phantom Hourglass where the corresponding four Cobble Knights rest, in them Link has to 1) find a way to the isle where Mutoh's Temple is, 2) enable said way in that island, and 3) enter the temple.
Pirate Stronghold in Skyward Sword, where Link has to find clues to track the next main dungeon, the Sandship.
The Spacestation in Jet Force Gemini. It's pretty much like the cargo ships visited by Juno, Vela and Lupus through their individual routes, but it's severely wrecked and the only relevant thing to do is to rescue Tribals.
Inverted in Star Fox Adventures. The first Plot Coupon Fox looks for is a Spellstone, so he makes his way towards one of the satellital regions of Dinosaur Planet to retrieve it. After he does so and gives it back to its corresponding Force Point Temple, the next thing he tries to find is a Krazoa Spirit, which lies within one of the Krazoa Shrines, and then puts it back into Krazoa Palace. In other words, he first goes to the dungeon areas and then goes to the mini-dungeons, the Shrines, which are little more than obstacle courses compared to the clusters of puzzles and obstacles that constitute the floating parts of Dinosaur Planet.
Metroid Prime 1 and 3 have, respectively, the sunken Orpheon Frigate and the wrecked GFS Valhalla as relatively large and intrincate mini-dungeons, which respectively precede the Phazon Mines and Pirate Homeworld as huge, gargantuam dungeons.
Ōkami has two: The Sunken Ship and the inside of the Water Dragon. The former precedes the Imperial Palace and even has the ítem that allows Amaterasu to get access to it. The latter is explored to get a magical Crystal Ball in order to give it to Queen Otohime and, right after its completion, a series of dramatic events occurs and leads to the entrance to Oni Island, the next main dungeon.
The entirety of Challenge Mode in Pikmin 2 is about exploring 30 miniature caves, most of which are only 1-3 floors deep, and derive from the Story Mode caves whose depths range from 5 to 15 floors except the Emergency Cave, which is a Noob Cave and thus another mini-dungeon.
The two areas of Vono Islands explored in The Last Story. Namely, the Mysterious Forest and the Shipwreck. They're explored before the Gurak Island, a main dungeon.
NetHack has a few side branches, such as the dwarf caverns, a couple towers and the quest.
Dragon Age: Origins had The Fade, the realm where spirits, demons, and dreaming human reside. You enter it completely out of nowhere, while exploring a tower where demons have overrun the mages within, and once you're in, you must complete it to continue. The stage itself is a repetitive puzzle maze, your player character is completely alone, there is next to no dialogue or plot progression, and the entire place is intentionally blurry and out of focus. It is so infamous to DA fans that several mods exist which allow you to bypass the mini-dungeon completely while collecting every reward from it.
The Brick Road dungeon in EarthBound is placed just before the cave leading to Rainy Circle, which contains one of the Eight Melodies.
World of Warcraft used to have several places commonly referred as mini dungeons or outworld dungeos. These were areas in the main game world (rather than being instances like proper dungeons), that othervise functioned similar to dungeons, with elite enemies designed to be fought as a group. They usually had quests associated with them with rewards similar to ones you'd get from actual dungeons. However, in later expansions most of the enemies in them lost their elite status, making them easier to solo and not any different from normal areas.
Aside from Bonus Stages, the first three games in the Crash Bandicoot series have special mini-stages that is accessed through special means: Collecting N. Brio or Neo Cortex icons (first game) and stepping on a colored platform or skull-patterned platform, aside from other things (second and third game). These stages - often called "Gem Routes" or "Skull Routes" - are much harder than the actual levels and rarely have a checkpoint. In the case of Skull Routes, you also have to reach the place without dying beforehand. Completing succesfully the Neo Cortex stages will net you keys that open secret levels; completing the Skull Routes will net you gems (in some rare cases colored ones, which are the ones that give access to the Gem Routes). The Gem Routes themselves only have regular gems as rewards.
Five hats means that five tropers think it is ready to publish.
You are saying that you think this draft is ready to be published. That means the description is not ambiguous,
it doesn't duplicate an existing trope, there are at least three examples, and the title makes sense.
Is that what you meant to do?
You are saying this draft has a ready-to-publish hat it does not deserve and you are taking it back.