Best to use stealth through this level to avoid large fights. Stick to the inside wall around the keep and you should make it to the walkways on top with only one fight in the cellar. Once up there, you can make a mad dash all the way left, then up through the covered corner area, and taking the first right, then the first left, you'll get shot at by a catapult and knocked into the dungeon. Head out the door to the right to complete the level.