Quilotoa is a crater three kilometres across in the Andes of central Ecuador, and the turquoise lake on its floor stands where the top of a mountain used to be. Around 1280, after some fourteen thousand years of quiet, the volcano erupted on the scale of Pinatubo in 1991. Ash fell across the northern Andes, and hot rock and mud ran as far as the Pacific. With the magma chamber emptied, the summit fell into itself, and the pit it left is what the water fills. The rim you walk today is the edge of that collapse, close to 3,900 metres. The last few steps up to it open the whole bowl: a turquoise disc held in sheer walls, Andean peaks standing beyond, wind hissing through the páramo grass. Come back at another hour and the same water has changed, bright turquoise at midday, deep emerald later, an almost-black navy under heavy cloud.
A steep zigzag takes you down the inside of the wall to the shore in about thirty minutes on loose, dusty ground. The way back takes one to two hours through thin air, and it is the real walk of the day. At the bottom a small dock rents kayaks, which is the only way out onto the water. Nobody swims. Gas rises through the lake from vents on the crater floor, hot springs seep out of the eastern wall, and on still days you can pick out streams of bubbles near the southern shore. Paddling at this height is harder than it looks, and from the middle the walls stand sheer on every side while the colour shifts under you. The rim village is also where the Quilotoa Loop begins. It runs for several days along ridge-top paths between terraced fields and open highland grass, linking Kichwa hamlets, with a night in each. The bowl does not end at the waterline. The lake is 250 metres deep, and the mountain that once stood over all of this went down into it.