Sumidero Canyon -- I am fastened to a zip line, gliding above the jungle canopy at about 50 km/h, when I notice a figure on a platform in the trees. It is Jorge, my guide, and he's waving his arms wildly.
Finally, I can make out his words: "Frene! Frene!" The brake! I'd been so captivated by the sunlight reflecting off the waters in the nearby canyon, I'd forgotten his instructions to apply the cable brake once he was in sight.
I'm at Cañon del Sumidero Ecotourism Park, one of southern Mexico's newest adventure destinations. In the state of Chiapas, bordering the Pacific Ocean and Guatemala, it offers some of the country's most diverse natural landscapes.
It's not only adventure here. Sumidero Canyon's vast limestone walls rise above the Grijalva River like a Mayan temple.
According to local legend, a tribe called the Chia resisted colonialism until 1532, and when cornered by the Spanish army threw themselves into the canyon's torrential waters rather than submit to Spanish rule.
In 1981, construction of the Chicoasén hydroelectric dam raised the river's level and tamed it, enabling boats to travel the 25-km reservoir now designated Cañon del Sumidero National Park.
To reach the park, I boarded in Cahuaré, an estuary draped with vines. As our launch motored along the quiet waters, we passed crocodiles the size of dugout canoes sunning themselves on large, submerged rocks. Hawks soared overhead.
Rock formations, sculpted over 12 million years ago, rose above us like skyscrapers. Hundreds of cave entrances were hidden in the shadows of the riverbank.
One grotto held a statue of the Virgin of Guadalupe. The face of Christ was visible in the rock's natural formation beside her. Deeper within the canyon, the rock formations were even more dramatic. One, covered in soft green moss, seemed bent under the weight of a cascade of water drops. Glistening in the sun, their crystalline reflections were like snow on the boughs of an evergreen tree. Rainbows arched across the canyon floor.
Despite the beauty, it was an eerie feeling to be drifting over the bones of thousands of warriors. Drawn deeper into the canyon by the current, the moist air seemed infused with a mystical quality.
Later I learned that the last warrior chief, Sanuime, was burned alive and his followers hanged nearby. Hidden among the trees are the remains of ceremonial centres dedicated to the water goddess Mandanda.
Forty-five minutes later, we've arrived at the entrance to Cañon del Sumidero Park. Built in 2003, it's still relatively undeveloped and encompasses only 6 of 197 hectares of protected territory. Tourists are scarce. In addition to hiking, the park offers mountain biking, kayaking and Mexico's longest canopy tour.
Deciding to try it out, I climb a wooden ladder to a platform high in a ceiba tree, where a guide helps me into a safety harness. He snaps it onto a large pulley that runs along a steel cable connected to a platform 800 metres away.
After a moment's hesitation, I leap out into the air. Swinging low, I zip along the steel line, accelerating with speed. Then too fast I come barrelling up to the next platform. Jorge grabs me to soften the landing and unclips the cable.
Once I master the brake, the remaining three zip lines are much easier. Whizzing along the treetops, I can relax and enjoy the mist rising off the cloud forest. Howler monkeys roar and fill the air with their shrieks.
Too soon, the canopy tour ends at canyon's edge. As I stand and gaze across the gorge, I contemplate the park's past.
The spirit of warrior chiefs and Mayan priests feels as alive as the that of the eco-adventurers of present.