We actually rented a car and drove. It was more expensive, but it gave us a lot more freedom. I may be wrong now, but at the time we went, the shuttle only ran once there and once back. So you're stuck there until time for the shuttle back. We were really excited to go and thought we would be there a full day. But we finished HOURS before the time the shuttle would have left. And then it started POURING (like, Noah's-flood-pouring). It would have been miserable if we had been stuck there for several more hours.
(Again, the shuttle process may be different now, but that's how it was when we went).