In Mexico's Yucatan Peninsula, a hidden underground world is under threat by the Maya Train

Engineer Guillermo D. Christy photographs a steel pillar filled with concrete that was installed inside the Aktun Tuyul cave system to support the Maya Train track on the outskirts of Playa del Carmen, Mexico, March 3, 2024. A passenger looks at the passing jungle landscape while traveling on the Maya Train from Cancun to Valladolid, Mexico, March 6, 2024. When it's completed, the high-speed Maya Train will wind around Mexico's southern Yucatan peninsula. A line of the Mayan Train is built using material dug out from the nearby tropical forest near Playa del Carmen, Mexico, March 1, 2024. When it's completed, the high-speed Maya Train will wind around Mexico's southern Yucatan peninsula. Workers build a Maya Train railway track near Playa del Carmen, Mexico, March 10, 2024. Engineer Guillermo D. Christy shows his hand stained with rust after touching a steel pillar in the Aktun Tuyul cave system. Construction of the Maya Train is rapidly destroying much of the hidden underground world of caverns and sinkhole lakes. A Mayan Train worker waits for passengers to board in Cancun, Mexico, March 6, 2024. ight shines through a hole made by massive metal drills to introduce a steel pillar filled with concrete that will be used to support a part of the Maya Train track, inside the Aktun Tuyul cave system on the outskirts of Playa del Carmen, Mexico, March 3, 2024. A hat sits on a Maya Train passenger seat en route to Valladolid, Mexico, Wednesday, March 6, 2024.

Rays of sunlight slice through pools of crystal water as clusters of fish cast shadows on the limestone below. Arching over the emerald basin are walls of stalactites dripping down the cavern ceiling, which opens to a dense jungle.