Hike Distance: 12.4 miles (20 km) round trip
Trailhead Elevation: 7,000 feet (2,130 meters)
Ostrander Lake Elevation: 8,500 feet (2,600 meters)
Total Elevation Gain: 1,600 feet (490 meters)
Trail Notes: The red line, as you've probably gathered, is the trail to Ostrander Lake. The white line is Glacier Point Road, which Google doesn't see fit to display at this zoom level, though they'll probably get things sorted soon.
The first stretch of the trail, pointing more or less due south, is mostly flat and takes you through a series of meadows and clearings. If your timing is good, it'll be awash in wildflowers.
Once the trail turns to the southeast, it begins a gradual climb to Ostrander Lake. Just past Horizon Ridge, you'll go through a high clearing with views all the way to the back of Half Dome. When you turn west again at the very end of the trail, it'll be your first notable descent of the day, off a ridge into the Ostrander Lake basin.