Corcovado

Declared in 1975 after a campaign led by the Costa Rican naturalist Mario Boza to stop logging and gold mining on the Osa Peninsula, Corcovado was described by National Geographic as "the most biologically intense place on Earth", packing an exceptional density of species into a relatively small area — including all four of Costa Rica's monkey species and one of the last viable jaguar populations in the country. It can be reached only by boat or light aircraft, with no road access, and since 2018 it has been compulsory to hire a guide to enter the park, a measure that has cut poaching markedly and improved visitor safety.