Austin is a blast, you'll love it!
Lots to do, a few suggestions:
1. 
Barton Springs to tan and swim/snorkel.
2. 
Hippie Hollow - Nude Beach (not really a beach, it's rocky but pretty.)
3. East side / East Dirty 6th st. for good bars and music (
Whitehorse bar is great for country music and dancing)
4. The Domain- for upscale shopping, food & bars (
Gloria's restaurant Saturday night Salsa dancing)
5. Downtown- 
Cheer up Charlies
6. South Austin:
  A. The 
Broken Spoke (local legend for country music and dancing)
  B. Guerro's or 
El Alma for great Mexican food and the best Margaritas)
San Marcos (25 minutes from Austin): float the crystal clear sp[ring fed river!
New Braunfels (40 minutes): Another amazing river and great night life