I spent two days at Iguazu Falls in 2014, after WMOC in Brazil. Those falls are the most amazing natural wonder I have ever seen. Highly recommended.
How was the orienteering?
The orienteering was several hours drive away from there, so I don't know whether what I experienced would apply. What I did experience was not to my liking: it was either jungle or plantations, and it was either raining or really hot and humid. But it was a great trip nevertheless, and capping it off with a visit to the Falls made it an amazing trip. Sharon and Brian Ellis won the Long Champs in their respective divisions; maybe they'd have a more positive view of the orienteering.
In all fairness, I'm not that happy with the weather in Washington, DC, either, so you might not mind Brazil.