Volcanic beach
There are lots of beaches around the lake Villarrica, but the most crowded, the coolest, the one where everything happens and where you'll be given free passes for clubbing, is definately the Hotel Pucon's beach. It's not really the hotel's beach, but since it's next to it, everybody knows it by this name.
One thing in particular. The sand in this beach is black. Not dark brown, but black. It's the volcano's dry lava from centuries ago. So do take shoes or sandals, 'cause it does get really hot during the summer.

Rio Liucara, near Pucon
Monitoring Volcanic Activity
Termas Geometricas-(post card)
Termas Geometricas-photos from Internet