The first room right next to the top of the stairs has a broken wooden door. If a thief notices or checks there was a strong lock on the door, but it is busted as well. The inside of the room is 15' x 20' and is piled with wood debris from broken furniture such as a bed, wardrobe and book shelves. In one corner is a chest, one would store blankets in, and in the other is the remains of a wardrobe.
In the wardrobe there is rotten clothes. If a search is done there is a small coffer inside with some necklaces and gems of various values, (up to the GM on values).
The chest is actually a mimic. Mimics have a +20 to disguise checks, so the Players need to roll against such DCs.
There are no secret doors or other ways out.