Deciding not to bust through a window, you circle around the keep. There are no more windows, but at the far side is an archway leading inside. It leads to a vast, empty tower that soars both up and down into darkness. From your position in the archway, you can see another archway to your right, leading into the keep. And across the way to the left is a doorway.
--- MAP ---
(My map sucks right here, but bear with me.)