One of the most interesting areas of Puerto Rico is the large Karst Country, south of Arecibo. This other-worldly group of rock formations were created by the process of water sinking into limestone. As time goes by, larger and larger basins are eroded, forming sinkholes. Mogotes (karstic hillocks) are peaks of earth where the land didn't sink into the erosion pits. The Karst Country lies along the island's north coast, directly northeast of Mayagüez in the foothills between Quebradillas and Manatí. The region is filled with an extensive network of caves. The world's largest radio/radar telescope dish, the 20-acre (8-hectare) Arecibo Observatory , rests within one of these sinkholes.
South of the Karst Country looms the massive central mountain region and Utuado at the heart of the massive Cordillera Central mountain range, which rides the island's back from east to west like an elevated spine.
The Karst Country area was deforested in the late 1940s; alluvial valleys and sinkholes were then used for pastures, shifting cultivation, and coffee plantations. In this region, most of the coffee sites were abandoned in the 1960s, and today most of these sites are covered with secondary forests. The recovery of these forests has been very rapid because of a close seed source -- trees left on the steep slopes -- and the presence of large populations of dispersers, mainly bats.
The only way to explore the Karst Country, which is easy to reach from San Juan, is by car. Leave San Juan on the four-lane highway, Rte. 22, until you come to the town of Arecibo, a 1 1/2-hour drive, depending on traffic. Once at Arecibo, take Rte. 10 south, in the direction of Utuado.
If you'd like a specific goal for exploring in the Karst Country, visit the Arecibo Observatory and the Río Camuy Caves, previewed above. However, you can also spend a day driving at random, exploring lakes and forests at your leisure. If you decide to go this route, make the commercial town of Arecibo your base. Although not of tourist interest itself, it is the capital of the Karst Country and the starting point from which you can drive south along many interesting and winding roads.
From Arecibo, you can take Rte. 10 south in the direction of Utuado, which serves as the southern border to Karst Country. Along the way, you'll pass Lagos dos Bocas, one of the most beautiful lakes of the Karst Country, and this is a reservoir adjacent to the Río Abajo Forest. Lagos dos Bocas, which lies 12 miles (19km) south of Arecibo, is in the mountains of Cordillera Central. Along with a nearby lake, Lake Caonillas, it is the main source of water for the North Coast Superaqueduct, which provides water for north coast towns stretching from Arecibo to San Juan.
Take time out at Lagos dos Bocas to ride one of the free government-operated launches that traverse the lake. Established as a taxi service for residents of the area, these launches can be used by sightseers as well. The launches leave from a dock along Rte. 123 on the west side of the lake, with departures scheduled every hour unless the weather is bad. It's a 30-minute ride across the lake to the other main dock. On weekends, modest wooden restaurants around the lake open to serve visitors, and the launch makes stops at them. Most have tasty snacks, fried turnovers and the like, and cold drinks. Rancho Marina is your best bet for lunch (entrees $11–$17) with basic Puerto Rican dishes, from red snapper filet in a salsa criolla to breaded rabbit in a tropical sauce. It’s open 10am to 6pm weekends and holidays. There’s even mango tembleque for dessert! The launch will take you back to your car, and then you can continue your journey.
You can head back down to Arecibo, and then take the expressway back to San Juan.
Get a Good Map -- Arm yourself with the most detailed map you can find at one of the bookstores in San Juan. The free maps dispensed by the tourist office are not sufficiently detailed and do not show the tiny secondary roads you'll need to traverse for a motor tour of the Karst Country.