The Blue Lagoon’s milky-blue colour comes from silica particles that nourish the skin. Photograph by Prisma by Dukas Presseagentur GmbH, Alamy This article was produced by National Geographic Traveller (UK). Bathed in the morning sun, the Kerlingarfjöll mountain range glows in shades of red and orange, shrouded by plumes of steam escaping from fumaroles. “It’s alive — Hveradalir,” says my guide, Boris Baniar, nodding towards a footpath that descends into the valley below.