Ik Kil is an almost perfect circle punched into the limestone of Mexico's Yucatán, with clear water twenty-six metres below the rim and roots hanging the whole way down to it. Everything here arrives from above. The roots belong to trees standing on the jungle floor at the top and reach the pool in long unbroken strands. In the rainy months the rain spills over the lip and runs down them in thin waterfalls. From up there it is a ring of water framed by green. Then a stone stairway cut into the rock winds down the wall, and the air changes as you go, the heat of the ground giving way to something cool that carries every voice around the shaft. Black catfish drift as dark shapes well below your feet, and the water stays crisp even at midday.
Above the pool, carved ledges stand out from the wall, and people jump from them into the deep centre of the well — the same drop that brought competition cliff divers to set their platforms on this rim three times. Toucans, parrots and cardinals call from the gardens planted around the opening, so the whole shaft holds a small enclosed world with its own birds. The well sits three kilometres from Chichén Itzá, and it is routinely confused with the cenote inside the ruins. That other one is where the Maya lowered offerings to Chaac, the god of rain, and where dredging brought up jade, gold and the remains of more than two hundred people. Nobody swims in that one. Ik Kil had its own rituals, and it is the one you get into. The light is the last thing that comes down: for about an hour around noon the sun stands over the opening and drops straight to the surface, and the water goes luminous green under the roots. The rest of the day the well is in shadow, with that circle of sky still twenty-six metres over your head.