The World of Capsule Monsters
The World of Capsule Monsters is the primary setting of the Yu-Gi-Oh! Capsule Monsters arc.
It is an alternate dimension where monsters live and in-series is the basis for the Capsule Monsters game.
A room in the Pyramid of Alexander contains a giant map of this world, used to play a game. Stepping on the map causes one to be transported to the world.
The edges of the world have invisible barriers. While it looks like there is scenery beyond the barriers, if one moves beyond a barrier, they see a realm of nothingness.