The scenery makes an impressive about-face a little over an hour after I hop into the van at my hotel in the heart of San Juan, Puerto Rico. Rather than sipping minty mojitos at the Marriott’s beach bar in the city’s chic, waterfront Condado neighborhood, I find myself clad in a helmet, harness and lifejacket, kicking through a tangle of grasses and ferns that crowns the top of a rural hill. And instead of navigating colonial-era streets overhung with iron-railed balconies, gazing out at the 400-year-old walls of El Morro, I sidestep a farmer’s wonky gate, turn a corner and catch a wide view of the sheer limestone cliff on the other side of the valley.

That’s the great thing about San Juan, an often-overlooked city that many Caribbean travelers know best as a layover en route to farther-flung islands: It’s a day-trippers paradise. By night, world-renowned restaurants serve seafood al fresco against a cosmopolitan backdrop. And by day, a diversity of adventures impossible to find together on smaller islands beckons from all directions while promising to have you back in time for cocktails. And since getting there only takes about two hours of direct flying time from Miami, San Juan makes an ideal weekend getaway.

From my hilltop lookout, I see a flood of foliage rising up the sides of the basin between these geographical high points like water approaching the lip of a bathtub, and to my left a narrow rut cuts a path through the emerald sea of trees, marking the beginning of a modest down-hike to the valley floor. Stepping confidently ahead of me, Karel Hilversum—a local caving and canyoneering guide—pauses occasionally to point out tiny orchids clinging to trees or the stems of tropical tubers sprouting from the ground. But after about a mile, he stops abruptly. His partner emerges from the underbrush and beckons us to follow. Moving gingerly off the trail, we come to the edge of a cliff plunging into the narrow river canyon, and Hilversum explains that we’ll rappel the rest of the way. I clip onto the climbing rope, lean back and ease myself down 45 feet of rock with a handful of soft backwards hops, dropping in the cool water. Once in the gently moving river, the going gets really easy. “Just kick up your feet and go with the flow,” Hilversum explains. This short stint of what he calls body rafting deposits us at a sharp bend in the river upon which the Rio Camuy spills from the snaggle-toothed mouth of a vine-draped cave.

One of the island’s largest rivers, the Rio Camuy regularly slips below the ground and resurfaces again like a sand worm as it snakes its way through the island jungle. And this particular section is the last of its subterranean runs, downstream from the popular and impressive Rio Camuy Cave Park. In honor of the river’s final return to the surface world, this passage carries the redemptive name Resurgence Cave.

Wading waist-deep into the darkened tunnel, I move carefully over the irregular bottom, testing each rock with my foot before putting my full weight on it. We fire up our headlamps, and Hilversum throws his beam onto the cave walls, illuminating prehistoric fossils embedded in the limestone, walking and talking as he gives us a geology lesson on Puerto Rico’s karst region. Soon we come to a side passage that sits above the waterline, and we move away from the river, at times crawling to squeeze under the cave’s low ceiling, and eventually emerging into a large chamber where we stop for water, pictures and to catch our breath in the damp air.

From here, we double back along another side passage, and the sound of moving water grows louder as we make our way back to the river. “Time for more body rafting,” Hilversum says as I slide down the embankment on my heels and hands, thoroughly covered in soft mud. In the interest of staying together, we all line up single-file, facing downstream. Each person holds the lifejacket of the one ahead, and in unison we kick out from the shore and lean back into the armchair position as the river sweeps our motley, muddy train down current. When the mouth of the cave comes into view, we stand up, the mud washed clean from our bodies and clothes, and I can’t help but feel that Resurgence Cave has lived up to its name. Even after a short time inside, the warmth and light of the sun filtering through the jungle canopy feels redemptive. The van is just a short hike away, and as promised, I make it to the beach bar by sundown—just it time for that mojito.

The San Juan Marriott’s activities desk arranges hiking, caving and rappelling tours of Resurgence Cave for $164 per person, which includes transportation to and from the trailhead, professional guides and all equipment.

Puerto Rico 10/25/09-10/28/09:

Rio Camuy Caving Expedition, San Juan Marriott Press Trip