The most awesome place I have ever been!
I visited Iguazu Falls the first time back in 1978. I stayed in a hostel that was just outside the park where international travelers stayed - no electricity and no plumbing in the rooms. The falls were so fantastic that I went back another three times, staying at the same hostel.
The natural beauty is unequaled.
Each night at dusk, thousands of little black birds (swifts?) flew to the "Devil's Throat", where the Parana River falls. They would dive way down, almost to the bottom of the falls and then shoot up on the current of mist to the top of the falls all singing at the top of their lungs!
It was so incredible that I went every dusk to witness it and then walked through the darkness that fell quickly on the jungle when the sun had set.
Once while walking back in the blackness, I saw what appeared to be a ball of fire with a long tail, like a comet,shoot through the trees. I learned from a local that it was a colony of fireflies traveling in a ball with the stragglers comprising the tail!
Another time I saw a small beetle on a leaf that had "headlights" that shone a spot of light in front of it, just like a car!
The falls were so powerful that the force and sound of the falling water could put you in a near trance, reminding you of how insignificant you are.
Truly an incredible place!