Subspace

Basics (as of DEMO 0.9)
The Subspace, which takes a similar design to Waterfall, starts at the end of the Ruins. It consists of the hub-like area which leads to the Ruins, Snowdin, and the rest of the Subspace, and three rooms aligned in a T shape.

The room that leads from the hub area is simple, and only contains a few signs and a minecart similar to the one found in the Waterfall area in Undertale.

Following to the left is a simple room, commonly referred to as the "The Wall". It is named for the huge wall, which is supposedly built by the Don't Forget team, a competing Undertale MMORPG group. Sans is also present in the room, and is an important part of the online feature, as he charges your phone so it can be used.

From the previous room, going down the southern path leads to the special room, which has a save point, as well as the entrances to the racing and PVP minigames farther down, also including the unaccessible Hall of Fame. Additionally, there is a secret path on the far bottom-left corner of the room, which leads to an invisible maze. Going through this maze can lead you to the elusive Gaster Hand item, which disappears from your inventory quickly after picking it up.