You're required to hop the Zion shuttle if you'd like to tour inside the park during the peak season. Normally, I'm not excited about park shuttles, but Zion's are incredibly easy to use. They're clean, reliable, and don't require a map to understand. Just hop on or off at any stop. The shuttles heading into the canyon will eventually end up at the Narrows trail head, while the shuttles heading in the opposite direction will eventually lead back to the visitor's center. You never have to wait long, and the entire drive offers a great view of the park.