Wonderfully preserved by the Conservation Trust (http://www.fideicomiso.org) since 1975, the Reserva Natural Cabezas de San Juan (787/860-2563 or 787/722-5834, weekends 787/860-2560) comprises 321 acres of untamed scrub and mangroves and 8km of reef-lined coast on the northeastern tip of the island. You’ll pass the gated entrance to the reserve just beyond the Balneario Seven Seas car park, but the guard will only let you in if you have a reservation: reserve a tour in advance, by phone or online: English tours depart at 2pm.
Laguna Grande dominates the lower half of the reserve, while the bush-smothered hill that rises over the northern section is topped by El Faro, the old Spanish lighthouse completed in 1882. It now houses a small visitors’ centre with exhibits showcasing the reserve’s marine and coastal ecosystems, including the bio bay – the highlight being bags of dinoflagellates that glow in the dark when shaken. Be sure to soak up the magnificent views from the observation deck on top.
General tours (by trolley bus; 2hr 30min) provide a brief taste of some of the diverse environments preserved here, starting with the mangrove forests that surround the lagoon (30 percent of the reserve), where a short boardwalk passes red, black, white and buttonwood mangroves and hordes of crab scuttle for cover. At Playa Lirios you get a chance to see the rocky coast and scrub and the three headlands that give the reserve its name (cabeza means “head”), before ending up at the lighthouse. Other than birds and insects, the only other wildlife you may encounter are giant iguanas, plodding through the undergrowth.