Congregation Island

Congregation Island is an area accessible from the letter Z on the Alphabet Tower.

Features
This area is an enormous floating island littered with an alarming amount of unique NPCs, almost all of which do different things. There are also large arches with eyes around the place as well. One of the many NPCs is a blue face that highly resembles Uboa from Yume Nikki towards the right of the area. Interacting with it will cause the screen to darken and all of the NPCs will turn into the Uboa-esque one, including the Z connecting the Alphabet Tower. They will stay like this until you wake up.

There is also a piece of cheese on the left side of the map. Interacting with it will immediately take you to a dark void with creepy cheese faces chasing you. There is also another piece of cheese in here. If you manage to get the cheese without being caught, you will be sent back to the island, whereupon a new NPC will be found by the enterance who will give you 255 moneys when interacted with.

Directions
Kubotsuki's Nexus → Nail Board → Alphabet Tower → Congregation Island

Trivia
If you go into the game's files and look through the NPCs, every single one of them has a different name.