Rules:

*You can teleport into and out of it at will

*It has a couple of plug sockets and can connect to internet from the region you teleported in from

*You can take objects and people with you

*As already stated, it is (3m)^3 (3m*3m*3m). The walls are plain plaster with a light in the middle of the ceiling. The pocket dimension is topologically toroidal, so if there weren't walls and a ceiling/floor (which you can actually destroy) you would loop if you went more than 3m in any direction. Gravity, then, is artificial and can be altered to anywhere from 0 to 2g from a dial on the wall.

Edit: additional specifications

*You can only teleport out to where you teleported in from.

*Time proceeds at the same rate inside the pocket dimension

*There is an eject button for those inside to get out if something happens to you