Big Boo's Fortress

Big Boo's Fortress is an area in B3313.

Description
Upon spawning, the player starts at the entrance of the fortress. The fortress itself is basically a maze, with most of its rooms being similar to each other, infested by Boos and Mr. Is. A so-called main room can be noted, guarded by the Mad Piano and full of bookcases. A door there leads to a library area, while a side opening contains the titular Big Boo.

Origins
The concept of the area likely comes from one of Greenio's videos (this and/or this), as most of the textures match up with it. However, the layout of the area seems to be an original creation, with the exception of the library room, which closely resembles the one found in Big Boo's Haunt from the vanilla game.

The music is the Underground arrangement from the Coincentration mini-game in Super Mario 64 DS, also used in the aforementioned video.

Stars
This area has 1 star to collect:


 * Collecting all 5 keys scattered throughout the course rewards the player with a star, which spawns near Big Boo.

Leading here

 * Plexal Upstairs: On the top floor, enter the door in an opening with the number 3 on it and a hole before it, then go down the hole and enter the Boo painting.

Leading away

 * Big Boo's Haunted Forest: Defeat the Big Boo and enter its cage. (This leads you to the small forest section.)

Trivia

 * This area doesn't have enough coins from a 100 coin star, however, considering that Big Boo's Haunted Forest can be accessed directly from here, and is also in course 14, the coin counter doesn't change while going through the two areas. This can be exploited for an easier collection of the aforementioned 100 coin star.
 * (0.9) In the Mirror Room, on the side with the Star, there's a set of double doors with the letter "L" above, and entering the doors switches your character to the other plumber.