Specifically because it's December, take a look at whitewater rafting in Chile on the Futaleufu River. Not cheap but looks absolutely amazing. (if it was summer

Specifically because it's December, take a look at whitewater rafting in Chile on the Futaleufu River. Not cheap but looks absolutely amazing. (if it was summer I'd suggest Middle Fork of Idaho's Salmon River, which I've done and strongly recommend!)