A 2,243-metre sacred mountain simultaneously holy to Buddhists, Hindus, Muslims and Christians – the pre-dawn pilgrimage climb brings all four traditions up the same illuminated stone staircase in the dark, lanterns bobbing, the cold air carrying the sound of devotional music from different traditions at once. At the summit, as the first light breaks, the mountain casts a perfect triangular shadow westward across the lowland plains below – one of the most extraordinary natural phenomena in Sri Lanka, and the reason people make this climb again and again.