We visited the Brazilian side first, with Shelly and an English guy from our hostel called Kevin.
Then 2 days later we went across to Argentina with Shelly and saw the falls from that side. We thought the Argentinian side was more spectacular although I think you have to see them from both sides to appreciate the size of the falls and the power of the water.
The falls here are created from ancient lava flows that reached this point and created a vertical drop to the earth that was not reached by the lava. Then a second flow of lava reached almost the same point, in some places creating a double drop, whilst in parts it is a single, higher drop.
There were hundreds of beautiful butterflies, toucans and heaps of curious (hungry) Coati's (Quati's) - scroll down to see one of them up close.