Iguaçu is one of the most magical places I have ever been. Despite the tourism and its remoteness (17h by bus from Campinas/São Paulo). What a place! Pure show for your eyes… And your ears. I visited the Park from the Argentine side, but both sides are worth it. The Argentine side is way cheaper, not only the entrance but also in terms of accommodation (Puerto de Iguazú, Argentina vs Foz do Iguaçu, Brazil).
There are many things to do in the Park. You can do the upper and lower walkways, to enjoy all the falls from different distances and perspectives; "Climb" to the Garganta del Diablo (literally, the Devil's Throat), in which after crossing a metal walkway over the immense Parana River, you arrive at the largest waterfall in the world; Excursions by boat, from a calm ride by the river (look for the jacarés!) to an intrepid trip to the foot of the falls to end up soaked to the bone; Visit less traveled trails, such as the Macuco trail, to experience the wildest side (we saw monkeys, turtles, toucans and even a tapir). This road leads to a waterfall away from the rest, where you can take a dip in a magical moment.
On the other hand, in the surroundings of Iguazú there are many natural treasures (both in Paraguay, as in Brazil, and in Argentina). If you have time, it is worth it to explore a little beyond the falls. We visited some small mines in Wanda, Misiones (Argentine). They are about 40 km from Puerto Iguazú. Only the landscape to get there is beautiful, leaving behind several interesting communities around the mines.