Thorbardin
From Unofficial Ansalon Wiki
In Game
Thorbardin was original built by Sargonnas, and featured many powerful items and mobs. Included was a quest for a one-time only awarded item, I believe it was the hammer of Kharas, though its been some time since then. Many items had their stats adjusted, but the area still has lots of great items and good places to level. It can be difficult to enter, as the only exit this writer is aware of is through mudhole, which killed the last character this writer sent into it.
In Story
Thorbardin is the biggest and oldest surviving Dwarven Kingdom. It actually contains a number of sub-cities within it.