The morning light in Tulum slices through skinny palms as a row of humming e-bikes waits at TAE Headquarters. You push the throttle and the town slips behind—colorful houses and the occasional stray dog—while the road tightens into a dust-slick ribbon through low jungle. After ten minutes the air changes: cooler, wetter, the limestone smell of karst earth. When the first cenote opens before you, it’s a hole in the world—an oval of deep, impossibly clear water fringed by roots and a ring of stalactites overhead. The guide hands you a snorkel and points to a column of light where freshwater meets freshwater, and you step in.