The wall around the grounds is stone, as are the warder halls and the novice/soldier quarters. You could certainly climb those, but they are guarded so you'd likely get caught. The city itself was built with the One Power, but...it *was* built with stone, and there's another squirrel-inclined character (*eyeballs Jaryd*) who crawls all over it Assassin's Creed style, so it's definitely climbable.
