Any tips on what you have to see?

Manuel Antonio is tiny, I'll say that much. It's very much an "end of the road" beach town. I spent a lot of time just walking around, and I never had a bit of bad food (aside from a fancy Chinese restaurant in San Jose). But I still remember the awesome breakfasts at Cafe Milagro! I'd also recommend a stop at El Avión. I'd also recommend that you check out La Mansion Inn.

Something else cool: You'll see monkeys and iguanas everywhere in Manuel Antonio. 

the third beach of Manuel Antonio Beach is the best beach and a bit hidden. The town is only hotels and restaurant for tourist no one live in manuel antonio

The Manuel Antonio National Parkis Costa Rica's smallest yet busiest national park. According to "National Geographic", it is one of the most bio diverse areas in the world. You wont experience any problem in finding as many hotels and restaurants as you wish. However, I will recommend those that, in my opinion, are the best.  El Gran Escape is not only the most popular but the most consistent in terms of quality and service. This restaurant does not serve marlin or other billfish. Other good seafood restaurant is El Avión which was built around an abandoned US military cargo plane. This restaurant is famous for its sightseeing (located strategically in a hill). Located inside the Hotel Makanda by the Sea you will find the Sunspot Bar & Grill (awarded 5 spoons and best of the best by The Tico Times Restaurant Guide of Costa Rica). It offers locally-sourced meats and fresh-caught fish and seafood.

Some of the best local food is served up in simple food stands or open-air restaurants known as "sodas". Such meals are cheap and typically delicious.

I am a 100% sure you will enjoy Manuel Antonio and my beautiful country!

Pura vida!!!!

This area of the country has high bluffs that overlook the ocean. Find a little restaurant that overlooks the water and enjoy some ceviche.