Horton Plains is a grassland plateau above 2,100 metres in the central highlands of Sri Lanka — cold, misty and treeless — and at one edge it ends in a cliff 1,200 metres high called World's End. The view off that edge has a deadline. Once the day warms, cloud climbs the rock face and closes it for good, usually by nine, so the loop of about nine kilometres is walked from the gate's opening in the dark. You cross open patana grassland while mist still lies in the hollows and frost crunches underfoot, silver streams threading between wind-bent trees. In the cool early hours sambar deer, the largest in Sri Lanka, step out of the forest to feed on the open grass, mostly unbothered by walkers. Then the ground simply stops under you. On a clear morning the valley and its tea estates lie spread out far below you, with the Indian Ocean glinting some eighty kilometres to the south.
On the return leg a short side path drops through mossy cloud forest to Baker's Falls, where a broad curtain of water crashes over dark rock into a cold pool. After the silence of the open grassland the sudden roar catches you off guard. The falls carry the name of Samuel Baker, later famous on the Nile, who tried to plant a European farming colony in these hills in the 1840s; the plateau itself remembers a governor of Ceylon. The forest patches hold one of the rarest primates alive. The Horton Plains slender loris is a wide-eyed nocturnal animal that clings to the misty upper canopy, photographed here for the first time in 2010 after years in which scientists feared it gone. It hunts insects in the dark, so nobody on the daytime loop will ever see one. Around nine the cloud starts up the rock face, and in minutes the drop, the tea country and the coast behind it are gone into white. The walk begins in the dark for exactly that reason.