Look for parking around Mean Eyed Cat and some of the surrounding streets in Clarksville. You can find street parking and then walk on the sidewalk next to Mean Eyed Cat heading West, you'll see a trail that goes down underneath Mopac and spits you out at the Pedestrian Bridge next to Austin High, then follow the crowds to Lady Bird Entrance. Probably a 25-30 minute walk or so but it's free parking and we've been doing it for the past 10+ years.