Answer:
In terms of natural landmarks: Angel Falls, Iguazu Falls, Venezuela's Tepuis, the Galapagos archipelago and the meeting of the Rio Negro and Amazon in Manaus would be my guess.
In terms of man made landmarks: Christ the Redeemer in Rio de Janeiro, Machu Picchu in Peru, the Nazca Lines, the Floating Islands on Lake Titicaca and the Moai statues of Easter Island.