Spent a summer in Costa Rica. One of the friendliest places I've ever been too. One of the most amazing times I had was at these hotsprings; they had these gardens with little streams that all flowed into this central pool. The pool had a swim up bar and I was there at night with my then girlfriend. In the background, while we sipped on our beers, there was an active volcano (Arenal) which was dripping with bright orange lava against the dark sky...very surreal. The beaches are nice, the food is good, but the jungle is one of the harshest I've ever been to: everything is slippery, wet, full of spines/thorns, or capable of a injurious bite. Very exhilarating.
I also went to Paraguay. Fun place but didn't do much exploring. Instead I spent the month with The Ache, a hunter-gathering group of people (several tribes) that were first contacted in the 50's through 70's. We mostly ran around the southern Amazon while the men hunted monkeys/peccaries/birds (anything with protein on it) and the women gathered grubs/manioc (anything with more protein or carbs), and I tried to look useful, pasty westerner that I was. At nights we'd sometimes sleep on the jungle floor and they'd tell me how one source (not their first source though) of mortality for them used to be predation from jaguars. That blew me away, given our number one source of mortality is cancer/heart disease. Getting eaten by a big-ass cat...what a way to go. But I did spend some time in the capital city of Paraguay and we also made it to Ciudad del Este in Brazil. Both cities have a real bustle about them. I much preferred the country.
I'm planning to go back to South America at some point once I can scrape up the cash. At the top of my list is Chile and specifically a visit to Everton de Vina del Mar, the Chilean football club that was founded by a bunch of Everton fans back in 1909. Other places I'd like to check out is the Old City of Cartegena in Colombia and the Tapui's in southern Venezuela.