Poás Volcano is the second-most visited national park in Costa Rica for one excellent reason: a gently active volcano (and its triplet craters).

Here, a turquoise lagoon—the most acidic lagoon on earth—fills the world’s second-widest crater (0.9 miles wide). A second crater, now extinct, houses Botos Lagoon, a cold-water lake. Trails wind through the park, connecting the visitor’s centre with the volcano’s craters, cloud forests, and other habitats.