This 2,700-meter stretch of limestone caves is thought to have formed some 15 to 20 million years ago, the result of both tectonic shifting and a forceful underground river. After their formation, the caves remained below sea level for a long amount of time. Finally brought to the surface following further tectonic movement, the caves were eventually stumbled upon by the Guatuzos aborigines. During your guided tour of the caves, you’ll see limestone rock formations, bats, monochrome frogs, fish, spiders, crickets, and a variety of marine fossils. You may get a little wet – due to the waterfall and river – so it’s advised to wear light, quick-drying clothes. The tour is led by a bilingual guide and lasts around 1.5 hours.