I recently went and walked the boardwalk at Lady Bird Lake. I parked along the street at these coordinates below:
30.243414, -97.719840
I then walked West for a couple of miles along the trail leading to the boardwalk. The boardwalk is built on the lake, letting you walk on it. I carried my Nikon 28-300 and snapped these pics along the way.
Overall the boardwalk makes for some interesting photos. Bear in mind though parking is tough in downtown Austin.