Located in northern Puerto Rico, Camuy River Cave Park’s "show" cave, Cueva Clara, or Clear Cave, contains various geological formations.
Located in northern Puerto Rico, Camuy River Cave Park's "show" cave, Cueva Clara, or Clear Cave, contains various geological formations. (Christine Dell'Amore, The Washington Post)

At our tour guide's mention of scorpion spiders, an uneasy murmur rippled through the crowd.

We were about to enter the labyrinth — a twisty dark corridor that weaves through part of the Camuy River Cave Park, a gigantic cave system in northern Puerto Rico. Large arachnids call this part of the cave home, and as my fellow adventurers and I felt our way through the blackness, I noticed a shadowy spot on a cave wall.

As I squinted more closely, an arachnophobe's nightmare came into focus: A spindly, fist-size scorpion spider — technically called a tailless whip scorpion — clung to the rock, sporting a set of long, spiny pincers. Actually neither scorpion nor spider, the animal looks fearsome enough for both monikers but is harmless to humans. My boyfriend, Brian, and I examined it by the glow of our iPhones, fascinated by this unique cave dweller.

Perhaps the largest of Puerto Rico's hundreds of caves, Camuy quickly captures you in its web of wonders. Rio Camuy, an underground river that's been carving out the nearly 11-mile-long cave for millions of years, still roars beneath your feet, and the park's "show" cave, Cueva Clara, or Clear Cave, is awe-inducingly enormous, with a ceiling about 17 stories high and hundreds of feet wide. Camuy — and much of northern Puerto Rico — is part of a karst geological formation, which consists of rocks easily eroded by water, such as limestone.

And considering how impressive the site is, it's surprising that scientists explored the cave for the first time only in the 1950s. (Archaeological evidence shows that prehistoric Taino people had visited the cave over the centuries.) In 1986, the area became the 300-acre Camuy River Cave Park, a protected area of the Puerto Rico commonwealth that offers guided walks to tens of thousands every year.

A tailless whip scorpion, locally called a scorpion spider, on a wall in the Camuy River Cave Park.
A tailless whip scorpion, locally called a scorpion spider, on a wall in the Camuy River Cave Park. (Brian Clark Howard, The Washington Post)

I was initially wowed by tourist literature saying that Rio Camuy is the third-longest underground river in the world — a fact I heard at the park itself — but when I contacted cave experts in Puerto Rico after my trip, they told me that's an out-of-date statistic from the 1970s.

Even so, Camuy is still very special, said Abel Vale, president of the Puerto Rico conservation group Ciudadanos del Karso, or Karst Citizens, in an e-mail. "The underground world of caves, and especially those with rivers with all their wonders in formations, are challenging places that most people will not have an opportunity to visit," he said. But Camuy, with its accessible gems, gives people the chance "to view part of that marvelous underground world."

As nature addicts, Brian and I decided to swap sun and sand for the subterranean and visit Camuy during our week-long trip to Puerto Rico in November. Heeding multiple warnings that the cave can close by noon due to rain or crowds, we rented a car early in San Juan and got to the park by midmorning, just in time to jump on the orange tram that ferries tourists to the cave's southern entrance.

Chugging downhill through a misty rain forest, I soaked in the green riot of lilies, ferns, vines and moss-covered trees — a very "Jurassic Park" experience, as a visitor described it later. We got off the tram and our guide, Jarliann Rodriguez Sanchez, walked our large tour group down a path, at the end of which I expected to enter the cave via a narrow passage. Instead, as we rounded the turn, the earth yawned open, showcasing a humongous cave, like curtains pulled back on a theater stage.

Stalactites frame an entrance to the Camuy River Cave Park.
Stalactites frame an entrance to the Camuy River Cave Park. (Brian Clark Howard, The Washington Post)

We took stairs down into the belly of the cave, staring upward at the ceiling, which was rounded like a hollowed-out pumpkin and studded with a thick row of stalactites — mineral formations that grow from cave ceilings like icicles. Stalagmites, in contrast, rise up from the bottom of a cave as water drips down.

Farther into the dimly lit cave, the temperature dropped into the 60s, and the sound of chirping cave crickets and dripping water bounced off the walls. High above us, bats — possibly the Jamaican fruit bat, one of the cave's resident species — swooped from roost to roost, among the thousands of the flying mammals that live here.

The cave had a reverential feel to it, sort of like being in Rome's Pantheon. But instead of wondering how ancient Romans had built such a perfectly shaped dome, I was thinking about how the Rio Camuy had shaped such beauty over the millennia; experts believe that the cave is a few million years old.

The imagination is your guide

"I just got a giant cave kiss," Brian said behind me, using the cavers' term for a drop of water that falls on your face.

Sanchez began pointing out the cave's various rock formations, which water and time had shaped into a human face, an elephant ear, a head of broccoli, a giant muffin and, for fans of "Pirates of the Caribbean," Davy Jones. She was also constantly reminding us to "use your imagination" to come up with our own interpretations: I thought that the black stalactites on the ceiling looked like a straggly beard.

Sanchez told us that many of the formations are still growing, ever so slowly, and that there are no plants in the cave — the only green stuff you'll see is the moss sprouting near the artificial lights that help tourists see the cave. I learned later that the cave does host some hardy fungi, though.

We followed the curving, sometimes slippery path through the cave out of its northern entrance, which is framed by long stalactites that hang over the opening like locks of hair. Before us towered a tall, lush cliff, and we peered over the edge of a platform more than 400 feet down to the Espiral, or Spiral, sinkhole.

After we left the cave, I asked Sanchez about her experiences with whip scorpions. She showed me a picture on her phone of one of the arachnids chowing down on a cave cricket, its preferred prey.

Waiting for the tram to take us back uphill, I chatted with tourists Kevin McAuliffe of Rhode Island and Dan Seaton of Memphis, who both thought that the cave is worth seeing, especially for families looking to escape the beach and educate their kids. "It gives you a different perspective" on Puerto Rico, said Seaton, who has been to the island a few times and is drawn back by its enjoyable food and people. "It's always kind of nice to get off the beaten path a little bit."

Making its way back uphill, our train made one last stop: at an observation platform overlooking the Tres Pueblos — or Three Towns — sinkhole, which, at about 400 feet deep and 650 feet wide, is big enough for one of San Juan's historic forts to fit into. Most of the giant crater's gray limestone walls were covered with thick vegetation.

We weren't done with sinkholes just yet. Bidding farewell to Camuy, we got back in the car and headed for the nearby Arecibo Observatory, a remote mountain facility that houses the world's largest single-dish radio telescope, a device that detects radio waves from space objects such as stars and galaxies.

Listening in on the stars

Scientists built the site here in the 1960s in part because of northern Puerto Rico's karst geography: A sinkhole is the perfect natural cradle for the radio telescope's main dish. Arecibo is apparently also a natural location for movies: The telescope has appeared in the films "Contact" and "GoldenEye."

"World's largest" sounds impressive on paper, of course, but it's not until you're standing before the telescope for the first time that you realize, "Wow, that's big." From the outdoor observation deck, the telescope's 1,000-foot-wide dish, or reflector, looked like an enormous contact lens that a near-sighted giant had dropped on the forest floor.

Made up of 39,000 aluminum panels, the reflector focuses radio emissions from space onto nearby antennas. A platform about 450 feet above the reflector contains more sub-reflectors that are supported by a network of steel cables. The whole shebang is offset by the most gorgeously green undulating mountains, which during our tour were tinted with the light of the late-afternoon sun.

Brian and I watched as the telescope's sub-reflectors moved slowly on a circular track on the platform, and we reflected ourselves on what all this unseen data from space might reveal. Arecibo has contributed a lot to our knowledge of the universe, including providing the first map of Venus and the first images ever taken of an asteroid.

In addition, from this spot in 1974, scientists from the SETI Institute, a nonprofit organization dedicated to the search for extraterrestrial life, beamed into space the most powerful and deliberate broadcast yet in that search. Visual depictions of DNA, a stick figure of a human, the solar system, some biochemicals crucial to life and the Arecibo telescope went hurtling into the cosmos.

No one has responded yet, but if aliens ever pay Earth a visit, they definitely shouldn't miss Puerto Rico and its caves.

Dell'Amore is a freelance writer in Washington. Her website is christinedellamore.com.


Puerto Rico insider's guide

Get there: AirTran, United and Delta offer one-stop flights from Denver International Airport to San Juan, Puerto Rico, starting at $539 round-trip.

Stay: Acacia Boutique Hotel, 8 Taft St., Condado, 877-725-0668, acaciaboutiquehotel.com. Eclectic hotel with a pool-size hot tub, a minute from the beach. Rooms from $125.

Hotel Rosa Del Mar, Route 2, Km. 86.6, Comercio St. 1777, Hatillo, 787-262-1515, hotelrosa delmar.com. Oceanview hotel not far from the cave park. Doubles start at $129.

Dine: Lechonera Rancho T, Highway 111, Km. 3.9, Lares, 787-201-8148. Specializes in the Puerto Rican classic lechon, or roasted pork. Entree plus drink and sides starts at $15.

El Buen Cafe, 381 Highway 2, Km. 84, Hatillo, 787-898-3495, elbuencafe.com. Fresh Puerto Rican coffee and homemade sandwiches. Entrees start at $3.50.

Do: Camuy River Cave Park, Route 129, Km. 18.9, Camuy, 787-893-3100. Wednesday-Sunday 8:30 a.m. to 5 p.m. $15, ages 4-12 $10.

Arecibo Observatory, Route 625, Arecibo, 787-878-2612, naic.edu. Wednesday-Sunday 9 a.m. to 4 p.m. $10, children and seniors $6.

More info: seepuertorico.com/en/

Christine Dell'Amore