Caño Island ($10 admission) is 17 kilometers off the western tip of the Osa Peninsula, directly west of Drake Bay.

It is of interest primarily for its importance as a pre-Columbian cemetery. Many tombs and artifacts— pestles, corn-grinding tables, and granite spheres (bolas)—are gathering moss in the rainforest undergrowth.

Caño Island gets struck by lightning more often than any other part of Central America, and for that reason was considered sacred by pre-Columbian peoples, who used it as a burial ground

The 300-hectare island is ringed with secluded white-sand beaches that attract olive ridley turtles. Among its residents are boa constrictors (the only venomous snakes here are sea snakes), giant frogs, a variety of hummingbirds, and three mammal species: a marsupial, the paca (which was introduced), and a bat. Surprisingly, only 13 terrestrial bird species are found here.

Snorkelers can see brilliant tropical fish and moray eels among the coral beds. Offshore waters teem with dolphins and whales.

A wide and well-maintained trail leads steeply uphill from the ranger station. Contact the Osa Conservation Area headquarters for information (tel./fax 506/2735-5036, pncorcovado [at] gmail [dot] com).

Most lodges in the region offer day trips. It is forbidden to overnight.