Río Camuy Cave Park, Puerto Rico

The Parque Nacional de las Cavernas del Río Camuy sits between the municipalities of Camuy, Hatillo and Lares in northwestern Puerto Rico, with the main entrance at Quebrada in Camuy. It is a network of limestone caves and underground waterways cut by the Río Camuy, the third largest underground river in the world.

The scale is mostly still unknown. Over 10 miles of caverns, 220 caves and 17 entrances have been mapped, and that is thought to be a fraction of the system: many experts believe another 800 caves are down there. Only a small part is open to the public.

The modern discovery is dated to 1958 and was first documented in the 1973 book Discovery at the Río Camuy by Russell and Jeanne Gurnee. That word discovery does a lot of work, though, because archaeological evidence shows the Taíno, Puerto Rico's first inhabitants, were exploring these caves hundreds of years earlier.

The 268-acre park built around the system runs tours of some of the caves and sinkholes and is one of the most popular natural attractions on the island.

Its recent history has been dictated by weather. Hurricane Maria struck Puerto Rico in 2017 and did enough damage to close the park for years; it reopened on 24 March 2021 after restoration work, closed again after Hurricane Fiona in September 2022, and reopened in February 2023 by reservation only. Anyone planning a visit should confirm the park is actually open before travelling, because that has not been a safe assumption for most of the last decade.

The river that made it is the reason the numbers keep growing. A system cut by the third largest underground river on Earth does not end tidily, and mapping it has been the work of decades rather than a single survey.