Limbo, also known as the 5th dimension, is completely white and is also used to trap damned souls.
Limbo is completely white and barren. There are no landmarks, structures, or any variation in the landscape whatsoever.
Limbo is the location where damned souls are sent. This is where the Watcher is banished after trying to kill the Ancient Evil. Leo is also banished here after escaping from the dungeon.