Starting with a visit to the Parque De Aves (bird park), we proceeded to the Brazilian side of the waterfalls – from here we saw the waterfalls from above and to the side, getting a great overview of the falls as a whole.
The next day we then visited the Argentinian side of Foz Do Iguacu where we had a boat tour and went directly under the waterfalls! – Whereas the Brazilian side was like an overview, the Argentinian side definitely gets you deeper into the waterfalls, you walk along side them, under them and then above them. If you can only do one side, do the Argentinian side!

We finished with a visit to the Marco das Tres Fronteiras (three frontiers) where Brazil, Paraguay and Argentina meet at the Parana river.
Full blog post here:

The second and third wonder in Foz do Iguacu