Princess Peach's Castle/Basement Gallery

The Basement Gallery is an anomalous area in Princess Peach’s Castle. It is located near the basement, and appears to be an art gallery, hence the name. This area is very ambiguous, as it's only recording is an unlisted video by the Youtuber Dawdu, though it has had other reports through text.

Description
The Basement Gallery's main room is described as hexagonal with tiles on the floor and ceiling with pink walls decorated with paintings and carpet leading to other doors and the center of the room where a certain object is reported, such as a sign, pipe, or both, with pillars scattered around. This sign usually greets the player to the area. The paintings are notable as they are typically anomalous paintings, such as a painting using an unused texture or a level's skybox.

The other rooms of the Basement Gallery are very similar to the painting rooms seen on the first floor of the castle, with only minor differences such as the textures from the main room or minor geographical changes so that the room is not identical. These paintings are notably commonly reported to be copies of the paintings seen in the main room for reasons unknown, though it may have something to do with the paintings usually not being seen in the base game.

There is a unique entrance area seen before entering the main room of the Basement Gallery that appears similar to the hallway leading to the courtyard and basement only seen in Dawdu's video, showing a hallway that splits into two, with a staircase leading up to somewhere and the other half leading to a door that leads to another hallway with a different wall texture with the door to the main Basement Gallery. Whether or not this is it's own area is unknown.

Sarasa Sahara
Sarasa Sahara is a level that appears to be associated with Sarasaland from Mario Land, hence the name. This area appears similar to Shifting Sand Land and anomalous desert levels like Dry Bones Desert and Dry, Dry Dunes, likely due to having the same theme. This level reportedly has several enemies from Mario Land, either standard enemies reskinned to look like enemies from Mario Land or actual new enemies, though these reports may be false. This level's stars are reported to be similar to these other level's missions, such as taking it from Klepto, as well as a red coin star.

Monty Molehill
Monty Molehill is a level potentially associated with the unused texture showing large hills seen in the Donjon level. It is described as a grassy plane with multiple hills resembling those from Super Mario World around the level that the player can climb, with multiple unique holes in the wall that Monty Moles pop out of, also similar to how Monty Moles act in Super Mario World. This level's missions are very vague, though some have reported having to fight a large Monty Mole (potentially Mega Moles, again from Super Mario World), as well as the common 8 red coins star seen in almost every level.

Big Bubbly Trench
Big Bubbly Trench is the final level most commonly associated with the Basement Gallery. It is a rather unique level, being described as a cylindrical area similar to Tick Tock Clock, though some report it is only in that shape due to invisible walls blocking you from walking out into the endless ocean around the area, though the player starts at the bottom on top of a sandy area and must jump onto large bubbles floating from the ground to the top, constantly jumping between bubbles as they pop over time, while hitting cap boxes to keep the Metal Cap or Frog Cap so that they can still walk, as if they swim they can't get the cap back and will end up drowning before they can swim to the top. At the top of the level the player can resurface from the water and find the level's Power Star. This level also has common water enemies such as Bubs, Unagis, etc.

???
The pipe shown in Dawdu's video presumably leads to a level or area, though what it leads to is not shown. This may potentially be the Eternal Fort, as BlackJoystick's tapes have shown a similar pipe in the 4th Floor that leads to the fort. However, this totally enigmatic area is also similar to the mystery area in Star Road, also documented by BlackJoystick. This area also could simply lead to something much more benign, such as a Bowser level "spooky-themed" course.

Gallery
All of these are from the video made by Dawdu.