The FC Basement (FC地下ダンジョン, FC Chika Danjon, FC Underground Dungeon) is an area accessible from the Tribe Settlement.
This area is a collection of staircases with maroon floors (that silence your footstep noises) and 8-bit music playing in the background. There are also a collection of various monsters inhabiting the different floors.
If you take the staircase near the red eye monster in the entry area, you will go to the Mini-Maze. Take the one all the way to the east however, and you will enter the main portion of the maze.
Keep climbing various staircases, you may come across one of them which leads to a monochrome area. Continuing up these stairs will take you to Monochrome Feudal Japan.
The star in the entry area, if interacted with, makes a noise classic gamers may find familiar...