The Karst Country and Arecibo

Across the north of Puerto Rico runs a belt of limestone that rain has dissolved into one of the finest karst landscapes anywhere: hundreds of steep rounded hills called mogotes standing over a floor of sinkholes, with rivers that vanish underground and reappear kilometres away. Roads wind between the haystacks through thick forest. One of those sinkholes was used to hold the Arecibo radio telescope, for decades the largest single-dish instrument in the world, which listened for pulsars and sent the famous message towards a distant star cluster in 1974; its platform collapsed into the dish in 2020, and while the great dish itself is gone, the site retains a visitor centre telling the story. The Camuy river caves run beneath the same limestone.

What you actually see

• The mogotes - the steep rounded limestone haystack hills and sinkholes.
• The Arecibo observatory site - the visitor centre and the story of the great dish.
• Río Camuy caves - the third-largest underground river system, beneath the karst.
• The winding karst roads - driving between the hills through dense forest.

When to go

December to April is drier and best for the roads and caves; the karst belt is humid and green year-round. The cave park has limited daily capacity and has had extended closures for repairs, so check it is operating before making the trip.

Honest expectations

The telescope itself is gone, and visitors expecting to see the famous dish will find a collapsed structure and an exhibition rather than the instrument; the site's future has been uncertain. The Camuy cave park has closed for long periods. Roads through the karst are narrow, steep and winding. It is a scenic and scientific day rather than a beach one.

Nearby

Arecibo and the northern coast are close; the Camuy caves and Lares are in the same belt.