Didn' stay in Rio but abaut 1.5h away by bus - in the mountains. Didn't see much of the surrounding but really got to know the people in a very small village.
Favourite spots:
The famous waterfalls of Iguacu. As far as I know the biggest - in this case: with the most water passing per time - waterfalls of the world. They are in Brazil and Argentina.
What's really great:
The parties in the evenings. In the European summer it's very cold in the South-Brazilian mountains, especially with missing heating. So everyone gathered in the two or three pubs and in front of them at a fire that was lit every evening.
Accommodations:
Prefer private
Other recommendations:
Don't stick to that city but enjoy some excursions out