Recommendation from Sebastian Wolff on the B4D Forum:

Many residents of Brasilia head straight out to Alto Paraiso or Pirinopolis if they think of beautiful waterfalls. And don't get me wrong, both places are very worth a visit. But you don't need to get that far for a nice hike and a refreshing bath in a beautiful tropical waterfall.

There are options around (and even within the city limits) of Brasilia. A nice area with many waterfalls is right north of the National Park of Brasilia. It is fairly easy to go there - although with some kilometers of dirt roads to pass - and guides and restaurants are in place.

For starters I have two recommendations. If you like a guided tour with meals included you should ask at the Chapada Imperial. They offer two or three different trails with more than 10 waterfalls and some nice canyons. It is possible to stay for the night in very simple but also lovely chalets.

If you like it unguided and are in the moot for a little adventure you can drive to the Poço Azul (blue pool) stationary. They've got two trails - one super easy - with up to four waterfalls to visit and of course take a bath in. The place can get a little crowdy on Sundays and public holidays.