Turtles call at Playa Grande year-round. The nesting season for the giant leatherback is October–March, when females come ashore every night at high tide. A decade ago, as many as 100 turtles might be seen in a single night; today, on a good night, a dozen might come ashore. (Olive ridley turtles and Pacific green turtles can sometimes also be seen here May–August).

Each female leatherback will nest as many as 12 times a season, every 10 days or so (usually at night to avoid dehydration). Most turtles prefer the center of the beach, just above the high-tide mark.

The beach is open to visitors by day at no cost, and by permit only with a guide at night in nesting season (6 p.m.–6 a.m., $25 entrance with guide; the fee is payable on leaving the beach if turtles have been seen); anyone found on the beach at night without a permit in nesting season faces a $1,000 fine (second offense; first offenders are escorted off the beach).

Guides from the local community roam the beach and lead groups to nesting turtles; other guides spot for turtles and call in the location via walkie-talkies. Visitors are not allowed to walk the beach after dusk unescorted.

Groups cannot exceed 15 people, and only 60 people are allowed onto the beach at night at each of two entry points (four groups per gate, with a maximum of eight groups nightly): one where the road meets the beach by the Hotel Las Tortugas, and the second at the southern end, by Villas Baulas.

Reservations are mandatory, although entry without a reservation is possible if there’s space in a group (don’t count on it, as demand usually exceeds supply). You can make reservations up to eight days in advance, or 8 a.m.–5 p.m. for a same-day visit. At certain times the waiting time can be two hours before you are permitted onto the beach; each night differs.

Resist the temptation to follow the example of the many thoughtless visitors who get too close to the turtles, try to touch them, ride their backs, or otherwise display a lack of common sense and respect. Flashlights and camera flashes are not permitted (professional photographers can apply in advance for permission to use a flash). And watch your step. Newborn turtles are difficult to see at night as they scurry down to the sea. Many are inadvertently crushed by tourists’ feet.

The park headquarters (Centro Operaciones Parque Nacional Marina Las Baulas, tel. 506/2653-0470, 8 A.M.–noon and 1–5 P.M. daily) is 100 meters east of Hotel Las Tortugas. It features an auditorium on turtle ecology. Viewing the film is obligatory for all people intending to witness the turtles nesting.

The Goldring Marine Biology Station (tel. 506/2653-0635, www.goldringmarinestation.org), next to Hotel Las Tortugas, is funded by the Leatherback Trust. Earthwatch (tel. 800/776-0188, www.earthwatch.org) has 10-day trips for volunteers, who are based at the station.