The falls themselves are the headline attraction, and most visitors structure their trip around the two main circuits inside Iguazú National Park — the Upper Circuit for the panoramic shots, the Lower Circuit for the spray and the close-up cataracts. The Devil's Throat catwalk, reached by the park's ecological train, is the single most overwhelming viewpoint. Plan on two full days to see the Argentinian side properly; a third for the Brazilian side; an extra for the boat trip under the falls.
Outside the park, Puerto Iguazú town has a handful of worthwhile stops — La Aripuca, the Güirá Oga wildlife refuge, the Triple Frontier viewpoint — and the Wanda gemstone mines an hour south make a decent half-day excursion.