The Refugio Nacional de Vida Silvestre Gandoca-Manzanillo covers the coastline south of Puerto Viejo as far as the Panamanian border — over 9,000 hectares of coastal forest, mangroves, coral reefs and turtle-nesting beaches. The trailheads are at Manzanillo, the small village at the end of the coast road.
A 4-kilometre coastal trail from Manzanillo leads through tropical forest to Punta Mona with panoramic views of the reef; longer routes continue along the coast to Gandoca village. The reef just offshore is the better of the two coral systems in Costa Rica, and several local operators run guided snorkelling trips from Manzanillo when the sea is calm.
Leatherbacks nest on Gandoca beach between March and July — fewer than at Tortuguero, and with far fewer people watching; guided night walks are organised through ANAI, the local conservation association. Dolphins are regular in the Gandoca lagoon, and dive operators rate the reef off Manzanillo above Cahuita's for coral health and fish diversity. Beyond Manzanillo the coastal trail carries on to Punta Mona, about three hours each way through increasingly wild forest.