The Stone World is a currently unfinished area in Yume 2kki, accessible only through a part of Geometry World. It currently has no exit, forcing you to either wake up or use the Eyeball Bomb Effect to leave.
Features
This unfinished area contains very little as of .94f, and what is there seems to be quite glitchy. Parts of the floor animate, and it is possible to get inside the walls at some points.
A solitary, buggy vending machine is also in the area. If you use it, it will take 100 money from you, transform into the small thing seen near some other vending machines, and make a strange noise.
Also of note is a ladder, hidden further inside the world. This ladder will take you to Monochrome GB World. There is also another flashing portal to the Digital Hand Hub in this world.
Connections
The Hand Hub (indirectly, one way)
Digital Hand Hub (One Way)