You can start at either end and make this trail an out-n-back. Starting from Lady Bird Lake, you'll travel through the city avoiding all roads and cars on a nice wide paved path. About halfway up, the trail turns to decomposed granite (an Austin favorite trail material).
Just past Pease Park, the trail becomes a bit more rugged. Towards the end you'll travel next to some steep cliffs that overhang above you. Just past the cliffs, you'll pop out at 31st Street. Have a little more in you? Head left on 31st Street, and after a few blocks, you'll see the trail picks back up on the left.
The trail ends at 38th Street, have a friend pick you up or head back down to the city and buy yourself an ice cold pint.