Last month when I visited Austin, we checked out Mount Bonnell. The river you see in the photo is the Colorado River and the houses lining the shores are HUGE multi-million dollar mansions. The roads along the river are sharp, curvy, and with the fancy houses it reminded me of Hollywood Hills, outside of L.A.
The whole area around Austin was gorgeous and I know that they have a few caves and hot springs. I really wish we had gone for more than a day trip so that I could have gotten some nice blue-hour photos. Its definitely on our list of places to re-visit.