Incredible white-sand beaches separate the park's protected seas from its vibrant forests that are home to 174 species of birds as well as countless other animal species. Mangroves and estuaries are plentiful, packed with a biodiversity known to few places outside of Costa Rica.

On Grande Beach (Playa Grande), female leatherback turtles come ashore to lay their eggs from October to May-an incredible spectacle to behold if you are lucky enough to see it. Guides are available for hire for those interested in this rare, but unforgettable opportunity.

Leatherback turtles are not only the world's largest turtle, but its largest reptile, which can weigh up to 2,000 pounds (900kg)! For all of their weight, these reptilian behemoths ironically have a pin-prick brain that weighs in at a measly 28 grams. Leatherbacks wander the open seas in search of their favorite food, jelly fish, which they will dive to a depth of 4,000 feet (1,220 m) to pursue. Unlike other species of turtle that have external carapaces, the leatherback has a tough leathery skin and internal skeleton.

Marino las Baulas National Park is just due north from Tamarindo. Driving to the park is best done in a four-wheel drive vehicle, as the road north of Grande Beach is rather rough and unpaved. An alternative to this route is by ferry across the Straight of Tamarindo. The process of making a reservation to see the Giant Sea Turtles is a little different than a normal tour and guide experience. Basically you can reserve a place on the list no more than 8 days in advance of the tour date by calling the Marino Las Baulas Station at 2653-0470 or from the U.S. it is 011 2506 653-0470. You must give them your complete name and passport number in order to be be put on the list. On the day of the tour you must arrive at the station of Marino Baulas at Sundown to pay for your ticket about $15 per person and be assigned in a group.

If there is a healthy nesting Turtle found by the biologists they will allow 1 group to come and view the process for about 15 minutes. Sometimes people must wait hours until a turtle arrives on the beach other times there are enough turtles for everyone to get a chance to view the nesting process. In some cases no turtles arrive at all. The Leatherback Turtle nests on Playa Grande from October to March but their numbers are drastically declining and in 2008 only 32 Leatherbacks came to nest on the beach.