Iguazú Falls are one of the most spectacular sights in the world. Depending on the season and water flows, Iguazú is made up of 150 to 270 subsidiary falls that stretch across a two mile area of Argentina and Brazil. The average drop from the top of the falls to the narrow canyon below is 240 feet (by contrast, Niagara Falls drops 170 feet on the Canadian side and less than 100 feet on the American side).
The falls can be seen up close (plan to get wet) by walking along the upper and lower "circuits" of walkways. Both are well worth traversing. The upper circuit is much flatter and an easier walk and offers wonderful panoramas and views looking over the falls. The lower circuit affords views looking up at the falls and also leads to a short ferry ride across to the Isla San Martin.
Across the Rio Iguazú, on the Brazilian side, is another hotel and more walkways offering what are said to be more panoramic views of the falls (I didn't go to the Brazilian side). The Brazilian hotel also operates helicopter rides over the falls that, from the Argentine side, are noisy and obnoxious and, according to Argentine naturalists, are disrupting the breeding habits of the many birds in the area. I was able to get a good view of the falls from the air on the commercial flight back to Buenos Aires, courtesy of the pilot who circled around twice so that all the passengers would be able to see
If you come anywhere near this World Heritage Site without visiting, you should regret it. I visited the falls as a two-night excursion from Buenos Aires and stayed at the Hotel Internacional Cataratas de Iguazú (now called the Sheraton Internacional Iguazú Resort), which was expensive but offered views of the falls from my room and was within easy walking distance (the only hotel on the Argentine side so situated; the others are in town, a good taxi ride away).