You may have been to Salto 脕ngel or Iguaz煤 Falls, seen Niagara or not even be particularly interested in waterfalls, but it doesn't matter: go to Kaieteur Falls. Watching 1140 metric tons of water shooting over a 250m cliff (the world's highest single-drop falls) in the middle of an ancient jungle with few tourists in sight is a once-in-a-lifetime experience.
Depending on the season, the falls are from 76m to 122m wide. The trail approaching the falls is home to scarlet Guianan cock-of-the-rock birds, and miniscule golden frogs (best seen in the rainy season and/or in the morning), which produce a potentially fatal poison.