On the northern border of Playa Nosara lies Playa Ostional, home to the Ostional Wildlife Refuge. The Refuge was created in 1984 to protect one the worlds most important Olive Ridley Sea Turtle nesting grounds. Year round the turtles will ride in at dark, during high tide, deposit their eggs in the sand, and head back out to sea. However in the rainy season, in a phenomenon called arribada, the turtles will come in by the hundreds, and sometimes even hundreds of thousands. This rarely-seen biological wonder is something not to be missed!