check it out.
Not much to say about Iguassu (or Iguaçu) other than go if you can.
There isn’t much to recommend the cities on any side of the triple border between Brazil, Arentina and Paraguay, except that they are close to one of the greatest falls in the world.
My only advice is to make sure you have at least 2 full days so as to have time to spend a day on each side of the falls–the Brazilian side offers the best overalll panoramic view, while the Argentinian side is much more intimate, with lots of little smaller falls, coves, etc, and more jungle to walk through.

Manuel Antonio is Costa Rica’s second most popular park (the first is a volcano).
Right on the coast, it boasts some of the area’s best beaches, protected offshore islands home to thousands of birds, and so many monkeys and sloth you’re virtually guaranteed to run into them. All of which has made the park so popular that a few years ago authorities decided to upgrade facilities, moving the entrance to a more central spot.
To get in, you ford a small estuary (rivulet at low tide), and although numbers are restricted, the place can be jammed on weekends in the high season (Nov-March). At peak times you actually have to wait in line unless you arrive first thing in the morning. The park is closed Mondays, closes fairly early (4 pm at writing), and costs 10 bucks a person.

But there is a back door of sorts to Manuel Antonio—which is good to know for several reasons. For one, if you happen to arrive at 3pm and just want to zip in and have a swim or look for monkeys, 10 dollars can be a bit steep. I am in no way condoning this, but in case you were wondering, the back gate is rarely monitored and you can easily walk around it.
Personally, I use the old entrance (which is what it was—the original entrance, now a service road) for two things: a more interesting way to leave the park than a long backtrack, and the best place to spot monkeys and other wildlife away from the crowds.
When we were last there I dragged my girlfriend this way and found ourselves quickly surrounded by Titi (Squirrel) monkeys, possibly the cutest animals alive; the only other people that came to join us were brought by local park guides.
To get to the old entrance from outside the park, take the last left turn before the park as you come into Manuel Antonio (at Marlin restaurant) and follow the road inland, staying right at the fork. There is a path around the right side of the gate.
If you come in the main entrance and just want some monkey action, walk to the far end of the popular protected beach and follow the service road up the hill for five minutes. At the crossroads, go straight to follow a trail to a great lookout or turn left and follow the road which eventually brings you to the old gate.

Before you begin to roll your eyes, let me assure you: butterflies are cool. Even if you don’t think you’ll find them cool—and I assure you, I didn’t—this place also has tarantulas, scorpions and seriously crazy-ass bugs you’ve never seen. For those of you who now think there’s no way in hell you’re going anywhere I’m talking about, give me a chance.
The Monteverde Butterfly Garden has always been one of my biggest surprises—I wanted to think it wasn’t cool, but every time I went, I found myself fascinated. So much so that on this, possibly my fifteenth visit to Monteverde, I chose to go back again, just to show my girlfriend Melanie how cool it was.
Plus, the staff—all student volunteers—really, really love bugs. By the end, so will you. I’ve seen these people turn even the most cynical tourists into a spellbound audience. Hell, hey even got my arachnophobic girlfriend to hold a tarantula. But I digress.
Started by a teacher, the Garden is eminently educational, and has something for everyone. With a little luck, you should even be able to release a newly-emerged butterfly on its very first flight. And if there were ever a more enthusiastic bunch of guides, I haven’t met them.
Monteverde Butterfly Farm (Jardin de las Mariposas)
Take the road from Santa Elena town to Monteverde Cloud Forest Reserve. At the corner where you pass Hotel Heliconia, veer right off the main road, past the ambulance station on your right and follow the signs.
Go mid-morning, as by late afternoon the butterflies tend to be less active and harder to see. Oh, and make sure to leave a tip for the guides (there is a shared tip box in the gift shop).