I may be wrong, but, I dont think you need reservations. It's just an "open air" thing sort of like the Sword in the Stone, if you're there, you get to be involved.
Location: If you walk from Main St. toward the castle, go to the right to go around the castle. When you cross the bridge you'll notice a walkway to the left to go back up to the castle. Dont turn left, and instead, look ahead and to the left and you'll see a little stone area. It's very nice. That's It I believe.