Zion and Bryce Canyon National Parks

Unless you are going in the winter, the only way to get into Zion Canyon proper is via shuttle (or ride a bike). In fact there is also a shuttle that runs into Springdale so if you are camped in town or at Watchman (recommended) in the park, you don't even need to move your vehicle except to explore the part of the park on the way east through the tunnels.

The shuttle at Bryce is convenient for hiking, as one can drop into the canyon at one trailhead and come out at another, utilizing the shuttle to get to/from your vehicle.