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
You say this pocket dimension connects to the internet, a la Matrix? I’d create a game with an in-game currency that looks the same as ours, and give it the same physical properties in-game as the real currency is for the region I’m in. I then would define that I am a billionaire with a bank account to match. I teleport in, withdraw my money in cash one suitcase at a time from the ATM that has an infinite cash supply, and then teleport out.
No, it’s not simulated. It’s a real place that just connects to electromagnetic waves from outside to have internet access.