The east wall rooms are completely carved out of the stone of the mountain side. Neither have doors and inside are two obvious library rooms. The bookcases, made of fine oak, are in pristine condition as our the books that line them. A desk sits in the north room, which is also in pristine condition, along with chairs and a table. In fact, even the ink upon on the desk is as fresh as if the vial was just set upon the desk. This pair of rooms has a stasis spell upon them. Everything is exactly how the wizard left his stronghold when he was fleeing the House Knights.
The surprise of this room are the skeletal knights which are summoned when someone walks through the door without the "key: tuned to this room. Since the "key" to this room left with the wizard. There is another key for other locks in the house in the cloak wardrobe in a chest if the party looks. The skeletal knights should be appropriate level for the party, so you may have to tweak the three that are summoned.
The skeletons have no treasure, but there are a lot of books in these rooms that can be hauled off. There are three spellbooks scattered around the rooms on the shelves. DC 30 to find each one. Spells in these books are up to the GM, though at least 50% should be necromancy.