Start at 7,214 feet and descend the Panorama trail toward Yosemite Valley. Beautiful views of the valley and waterfalls like Illilouette Fall. Continue via the John Muir Trail and Half Dome trail to the top of Half Dome for a 18 mile round trip.
Start at Glacier Point for a downhill hike (remember, you'll need to hike back up!). Take Wawona Road to Glacier Point Road to the end.
http://www.tripleblaze.com/trail.php?c=3&i=8534