Figured it out. Go to the top of the stairs, and there are two columns, and you'll see some tightropes that the wolf can walk across. Look at the column on the left when you're looking at the castle, and you should see a clawshot target. Get up there, drop down, and there's a spinner rail, and you go on that and jump off in the middle and you should land behind the chest. It's 100 rupees. If you go back to hte top of hte left tower, you go across the rope, then hang across the edge as Link and make your way over to the other column, there is another 100 rupees.