The trail starts out in a forest of aspens. You then pop out at the bottom of a very tall moraine. The trail zig zags up the moraine, ascending 1.4 miles. Views of the mountains are all around. You'll then be in a forest again and the lake is straight ahead. There's also a trail that goes all the way around the lake and through the trees.
Enter Rocky Mountain National Park from the main entrance at Estes Park. Go past the Beaver Meadows Visitor Center and turn left onto Bear Lake Road. Follow this road until you come to Bierstadt Lake Trailhead on the right hand side.
http://www.tripleblaze.com/trail.php?c=3&i=3147