A city of limestone towers rises in western Madagascar.


Unexplored passages shelter some of the island's—and the world's—strangest species, from the ghostly Decken's sifaka, a lemur, to a host of reptiles, insects, and plants.


Slot canyons and wet caves cut through the neighborhoods of limestone towers.


Climbers Luke "Fumakilla" Padgett and John "Razor Sharp" Benson descend a wall of limestone in Tsingy de Bemaraha national park and reserve in western Madagascar. Sharp, steep, and brittle, the protected area's maze of sunbeaten rock has repelled all but a few explorers and scientists, leaving large parts of the region—and countless resident creatures—unknown to humans. "I've never climbed anywhere like this," Benson said. "If you fall, even a few feet, you get impaled."


Benson weaves through skin-ripping pinnacles. In Malagasy, the formations are called tsingy, meaning "where one cannot walk barefoot." The terrain resists intrusions from hunters, hungry cattle, and wildfires.


Sunlight rakes the heights of the tsingy, where any rainfall is quickly shed. The arid upper reaches favor mobile creatures such as dragonflies (here in a cooling posture).


Spiny, drought-tolerant Pachypodium plants also thrive in the tsingy's top reaches.


Vertical pupils identify a seseke, or leaf-tailed gecko, as a nocturnal creature. Its camouflage works so well that the lizard doesn't hide during the day. It simply flattens itself against tree trunks while waiting for darkness and insects to eat.


Troops of Decken's sifakas, found only in western Madagascar, cruise the tops of the tsingy searching for food and evading predators. Like other lemurs, they probably live in small family groups.


Fearless acrobat, a Decken's sifaka leaps a chasm a hundred feet deep.


Blurring through the void, the Decken's sifaka sails across the canyon. Among Madagascar's largest lemurs and one of the tsingy's signature species, sifakas regularly jump along the jagged skyline as they range between fruit trees.


The leaping lemur comes to rest on a splinter of stone. Little is known about the behavior of Decken's sifakas, but evolution has equipped them with thick pads on hands and feet, helping them navigate their serrated home.


The Milky Way sparkles above slit-topped canyons as a nocturnal gecko hunts for insects. Scientists who visit the tsingy often go on "night spots," hikes through the dark forest to look for unfamiliar creatures such as fist-size cockroaches. "In a way this area is very representative of the whole island of Madagascar," says herpetologist Hery Rakotondravony. "There are many kinds of environments here and many kinds of species. It's very rich. There's a lot to discover."


An aerial view of tsingy formations reveals rows of tall limestone towers and deep, straight canyons—a landscape that resembles dense city blocks. The top of the tsingy is arid and bare, while the canyon bottoms, shielded from the desiccating sun, collect rain and soil. The city comparison isn't far off: Different animals live at different levels within the vertical habitat provided by the stone high-rises. Desert-adapted creatures command the heights while moisture-lovers prowl the damp shadows below.


Often no wider than a hiker's shoulders, slot canyons swallow water in the rainy season, funneling much of it to underground chambers. The passages remain moist year-round, supporting dozens of species of invertebrates and amphibians.


Most local people who enter the tsingy seek the sweet prize of honey.


Nightfall does nothing to soften the spiny ramparts, yet cooler temperatures and rising humidity entice many nocturnal creatures to emerge. Says biologist Steven Goodman, one of the few scientists to make repeat visits, "We've just touched the surface as far as finding out what lives there."


A Decken's sifaka peers out from a jagged stone maw. The tsingy region is a lemur hot spot: Several species inhabit the canyon forests, including the brown lemur and endemic nocturnal lemurs—the tiny mouse lemur and John Cleese's woolly lemur.