The Marino Las Baulas Marine National Park covers Playa Grande, Playa Ventanas, and the wetlands of the Tamarindo estuary. Its most famous inhabitants are the leatherback turtles that come ashore between October and March to lay their eggs in the sand. Tours run at night and are tightly controlled — small groups, no flashlights, no photography. It is an extraordinary experience: a thousand-kilo prehistoric reptile heaving herself up the beach a metre at a time.
By day the park is a much quieter affair. Playa Grande, the long surf beach across the estuary from Tamarindo, has a few small restaurants and almost no crowds. Boat tours up the estuary cost a fraction of those run from Tamarindo itself and give you crocodiles, herons, howler monkeys, and a peaceful glide through the mangroves. Take the small ferry across the river mouth from Tamarindo, or drive round via Huacas.