The guards won't let me in without fighting them, which I'd rather not. Is there another way in?
2 Answers
Yes!
Go around to the West of the tower (left from the drawbridge). There are vines hanging down the castle walls. If you click on them, you'll be able to leap across the moat, grab the vines, and scale the castle walls.
Also, you can go to the east of the stronghold and walk across the rocks that have fallen into the moat. There is the grate where Kolsc's guys went in first. If you have the prybar you can enter that way.