SIAN KA'AN BIOSPHERE RESERVE, Mexico - The Maya called this part of the world Sian Ka'an, or "where the sky is born." As we cruise across the milky green water of Laguna Campechen, part of the Everglades-like expanse of the eastern Yucatan Peninsula, the sky seems immense. A high scrim of clouds does little to shield us from the powerful sun; it's just midmorning, but the day is already very hot. The breeze in the open boat is mercifully refreshing.
Eight of us - a half-dozen visitors, our guide, and the boat's captain - are headed for the far shore, which from a distance presents itself as a low wall of mangrove. Our destination is the Cayo Venado, a 6 3/4-mile waterway that snakes from the brackish coastal lagoons to a series of large freshwater inland lagoons - the same route used by Mayan traders 2,000 years ago to move goods from the jungle to the sea.
We reach the other side, and Cosme, our captain, a short, stout Mayan man wearing wrap-around sunglasses, guides the narrow boat into a break in the mangrove, the mouth of the Cayo Venado. We're suddenly surrounded by vegetation, and the sky seems to shrink a bit. Tall, flowering bromiliads wave high above us. The farther upstream we travel, the narrower the passage becomes. Mangroves give way to expanses of savannah grass as the water becomes fresher. Ben, our guide, points out a pair of nesting osprey, and a large dark turtle tumbles off the bank into the stream. Cosme swings us around a bend and the stream narrows again, so much so that the lower branches of the scrubby savannah trees reach from bank to bank. Gliding beneath them is like momentarily being swallowed by this vast, elemental landscape.
Which is why we've come. We're on a daylong tour of the 1.3-million-acre Sian Ka'an Biosphere Reserve, the largest protected natural area in the Mexican Caribbean. Established by the Mexican government in 1986, the area is home to hundreds of bird and mammal species, from roseate spoonbills to jaguars, crocodiles, spiny lobsters, land crabs, and a teeming population of lizards. There are 23 known archeological sites, some more than 2,000 years old; Sian Ka'an was named a UNESCO World Heritage Site in 1987.
Our tour is organized by Centro Ecologico Sian Ka'an, or CESiaK, an education and ecotourism center located in the reserve, near the town of Tulum, about two hours south of Cancún. CESiaK was founded in 2000 by Cameron Boyd, a 34-year-old Lexington native who fell in love with the area and never really left. Boyd bought the oceanside property in 1998, and built his low-impact "centro" atop the ruins of a former oceanside Cancún-style luxury resort. The center, which opened for business in 2004, includes a main administrative building with a kitchen and dining room, 15 guest cabins, and a new multi-purpose space that hosts conferences, weddings, and yoga sessions.
Instead of boutique shopping and poolside pina coladas, CESiaK offers its clientele wetland tours, kayak expeditions, and fly-fishing adventures, as well as a working example of how development can tread lightly on a fragile ecosystem.
"The Sian Ka'an is one of the most beautiful and special places I've ever seen," says Boyd. "The idea with CESiaK is to live in a way that leaves a very small environmental footprint, while funding programs in environmental design, environmental education, and sustainable development. I think we've gotten pretty close to that vision."
The natural charms of the Sian Ka'an and the allure of the popular Mayan sites at Tulum and Coba drew my wife and me to the Yucatan's Riviera Maya for a week-long stay at CESiaK last May, between the peak tourist season and the start of the summer rainy season. We flew into Cancún and stayed a couple of nights at El Rey del Caribe, a charming, ecofriendly, downtown hotel that happens to be around the corner from a grocer with an encyclopedic selection of tequilas. Our shopping complete, we pointed the rental car south, eager to explore the Sian Ka'an.
Like the Cayo Venado, the road out of Tulum toward CESiaK gets smaller, then smaller still. At the stone archway that marks the entrance to the reserve, the road goes from paved to dirt. But the scrubby jungle on either side is lush and dense, and parts occasionally to offer views of the sea and deserted white-sand beaches.
CESiaK is perched atop dunes that crown the Boca Paila peninsula, a ribbon of land that separates the Caribbean from the lagoons of the Sian Ka'an. The laid-back rusticity of the place is a sharp contrast to Cancún's sprawling overdevelopment and monolithic resorts. Each "cabin" is a spacious furnished tent that includes a bed, wardrobe, a couple of chairs, and plenty of room to move around. The tent sits atop a raised wooden platform and is covered by a dense thatched roof. Hammocks hang between supports on the large covered porches.
In keeping with its green ethos, CESiaK's electricity is sun- and wind-generated, and it employs a comprehensive wastewater treatment system. Bath facilities are shared, and the composting toilets are surprisingly plush. There's no pool; for a swim, we made do with the Caribbean, steps from our cabin.
Local women cook three meals a day for guests and visitors, and the food is excellent. We ate breakfast on one of the building's terraces overlooking Laguna Campechen, and marveled at the bird activity in the trees below while enjoying our fresh fruit, yogurt, and strong coffee. For lunch, we ventured to eateries up the beach to sample varieties of the local ceviche. In the evening, we made the 20-minute drive into Tulum for dinner at one of the town's casual restaurants, where locals and visitors mingle over bottles of ice-cold Mexican beer.
Out on the Cayo Venado, Ben is inviting us to hop into the stream for a float. We've strolled around the small temple that marks the turnaround point of the trip, and we've contemplated the startling cobalt-blue water of nearby Laguna Muyil, which meets the Yucatan's interior jungle. But I've seen enough pretty water; now I just I want to get in. This far up the cayo the water is clear and fresh - and crocodile-free.
Cosme picks us up 30 blissful minutes later and whisks us back through the Cayo Venado, then detours through more large lagoons. In the middle of Laguna San Miguel, it appears as if the surface of the water is bulging upward. In fact, it is. Ten feet down, we can clearly see a large dark hole in the floor of the lagoon - the mouth of a cenote - around which are cruising schools of fish and dozens of large rays. Water is being expelled from the hole with enough force to create that discernable dome on the lagoon's surface.
The Yucatan sits atop a limestone plateau filled with caves and reservoirs through which courses the region's vast water supply. Cenotes are surface openings to this fantastic underground labyrinth. The Maya attached spiritual importance to cenotes, and organized their sprawling cities around them. The limestone extends into the sea, and incoming tides can push water rapidly through the passageways as they move inland. If a passageway happens to empty into a lagoon like Laguna San Miguel, the result can be spectacular. We stare down at the gliding rays for a few minutes more, then Cosme wheels the boat around and heads for the CESiaK dock.
We aren't quite finished with cenotes today, though. After a lunch of enchiladas, we climb into a van that shuttles us to the reserve's entrance. A short walk through the jungle brings us to what appears to be an oblong-shaped pond, surrounded by low, scrubby oak. Ben hands out masks and flippers, and we jump in. The pond itself is a cenote, filled with small tropically hued fish. The water feels soft and fresh, another respite from the afternoon heat.
Unlike most cenotes, which plunge straight down into the earth like giant wells, this one has a pond-like bottom, with its mouth opening at one end like an underwater cave. I skim slowly across the surface, gazing down at the large jagged opening below me. Bits of vegetation flow lazily from the mouth, the only sign that the water is moving. The opening is pitch black and a little creepy, and I recall how the ancient Maya regarded cenotes as portals to the spirit world. Cave divers revere the Yucatan and its porous limestone, but I prefer life above ground. The Sian Ka'an is about sea, lagoon, and sky, and it's for those that I'll return.
Scott Sutherland, a freelance writer in Boston, can be reached at email@example.com.