Pucón, often nicknamed the "Aspen of Chile," is a small tourist town at the base of the beautiful Volcan Villarica, located in the lakes region of Chile some 800km south of Santiago. Here you'll find practically every outdoor adventure you could imagine, including rafting, mountaineering, hiking, hot springs and of course, climbing. In the summer (January-February) and during Easter weekend expect huge crowds. Shoulder season from March through April can be excellent though don't be surprised if you get rained out (why do you think everything is so ridiculously green?). The food is amazing and diverse (try the salmon), accommodations are nothing short of posh, and the outdoor outfitters are skilled and really deliver an unforgettable experience. Don't forget to travel to the nearby village of Curarrehue to experience a little bit of Mapuche culture.
Buses depart from Santiago pretty much any hour of the day and TurBus seems to have the best deals for Pucón. As the ride lasts about 12 hours I recommend taking an overnight bus (about 8pm) so you can sleep through the journey and wake up refreshed and ready to send hard. Not a bad idea to drink a bit of excellent Chilean wine before the trip.