Check out the cells opposite of of yours for loot and then proceed. As you move out of the cell block, Serena mocks the knights who come out to attack you. Straight ahead there should be a sort of torture chamber. There's a battle axe in there that would make a good weapon for Erik to use. Follow the corridor left, fighting past guards until you enter another cell block and another torture room.
Stairs lead up from here, and the walls change from gray to red.
There's more cells here. Beyond these rooms stairs lead upward to the next level. Kill them and search the 4 rooms for weapons and cash you can use. The exit is at the far side of the room farthest from where you entered. Climb a staircase and you'll come out into a corridor that overlooks the beginning of the level.