Indeed, that's one of the many parallel dimensions (or PDs) in the game. You can read more about PDs and other useful things in the
FAQ for new players.
You can also see a list of every PD, with advice and (usually) demonstrative videos on
Cadomax.
PD11 can be tricky because it has some enemies that don't appear until much later in the normal game. However, once it gets easy for you to reach Level 50 or so, you'll find PD11 quite manageable.