From the park's website:
Difficulty:Strenuous; Distance 12-14.5 miles round trip
Begin at Basin Trailhead
This challenging trail is well worth the 2,000 foot gain, as midway are the stunning vistas from the South Rim. Ascend either the steeper Pinnacles or more gradual Laguna Meadows Trail. During Peregrine Falcon nesting season, the Northeast and Southeast portions of this trail are closed.
Click HERE to read Backpacker magazine's online trail guide to the South Rim.