MEXICO CITY - Morning dawns on Mayan lands, north of the Yucatan Peninsula. The sun illuminates a giant poplar that guards a secret beneath its roots: the cenote of Kankirixche, a cave with a pool of crystalline water reaching 50 meters down.

Inside this wide pit of stone, catfish swim in the deep as swallows nest in the ceiling made of stalactites. Everything seems nature-made, except for a 35-step wooden staircase that serves to access the spectacle.

Outside, Jose Arceo Ku Ucan, a 62-year-old Mayan citizen, receives visitors and charges them 20 pesos (around $1) to enter. He said the cenote was a secret until two years ago when the small community of Uayalceh agreed to open it to the public.