The enemies in the common area will be wights and undead. The layout of the area will be similar to the other areas you have completed. Be prepared though since there are two gorecyclops here. Don't underestimate the mages here as well since their High Maelstrom can easily wipe out your party. If you're unlucky enough, the Reaper and/or three Garms will make an appearance as well.
The second level terrace has some chests so you may want to levitate/ double-jump to reach them. There's also a recollection tablet inside a small flooded room to the west, accessible through the second floor or the hidden, vine-covered path in the first floor.
Once you're done looting the area, continue north and go downstairs. Be careful of the leapworms that will drop from the ceiling. Continue forth until you reach the door to the next area.