Isla San Martín sits in the Argentine side of Iguazú Falls, surrounded by spray, forest, and the roar of water. When access is open, the island changes the scale of the falls: you are no longer just looking across at curtains of water, but standing inside the river landscape between them.
Access depends on river level and park operations, so do not build the whole day around it without checking locally. If boats are running, the island is one of the best add-ons to the lower circuit, especially for travellers who want a closer, wetter angle on the falls.