Isla San Lucas, a short boat ride from the Puntarenas ferry terminal, was a prison island for over a century before being converted into a wildlife refuge in 1995. The ruins of the old prison buildings still stand among the trees, giving the island an eerie, atmospheric quality that sits oddly alongside the wildlife and the turquoise water.
The island has good snorkelling, healthy forest, and a range of birds and reptiles — but the prison ruins are what make it distinctive. Half-day boat tours run from Puntarenas in the morning; ask at the docks or at any of the tour agencies near the ferry terminal. The tour typically includes a guided walk through the ruins and time for swimming.