"But I stabbed a man in Imajapoor, just to watch him die" - popular song in Imajapoor by The Bard In Black
Foulsome Prison is where they throw you when they want to forget about you. You don't necessarily have to do something immoral or against the law to get sent there. In fact, Imajapoor was built upon criminal activity. But if you don't pay off the right people, you might find find yourself shackled to a 40 pound iron ball inside a 4X8 cell with three other room mates.
Getting out of Foulsome can be a bit tricky too. There's plenty of guards inside and on the walls of the prison, plus several beasties guarding the courtyard. If you can get to the storm sewers that would be your best route, but they lead to the mazes of the Underdrek!
Best thing to do is lay low, and keep a low profile when visiting Imajapoor. At least until you have enough geld to pay bribes, or enough muscle to not worry about paying bribes!
Keep on Rockin' & Role Playing!