Nowadays its easy to become caught up in suggested places to travel. There are so many guidebooks and magazines available, that they seem to litter the universe with suggestions. Take the fact that everyone wants to go to Machu Picchu, and though they should because it's amazing, after a while won't it become so routine that there's no real sense in going? It's like Everest, is it worth driving an area to the point of destruction in order to make it more available to tourists?
I can be extreme about nature, but it's worth the thought. As a mountaineer, I have my own personal agenda, and it is generally all about going to places that are remote in order to get some good climbs in, but also to bring increased awareness to the area.
Modern adventure travel needs to add a defined sense of purpose to travel. South American has tons of untouched places that need to be explored and then locked up in rock solid conservation trusts. Take a look at Access PanAm.
So, if you're an adventurer, pick a place that is untouched and unknown by most. Go with a local guide company and experience a trip that very few will ever experience. Bolivia's Cordillera Apolobamba is on my list, "El Dorado" is supposed to be close by.