Lake Toba is another of the island's spectacular sights - a remarkable volcanic crater set in the middle of northern Sumatra, 176km from Medan. The lake is huge (the largest in South-East Asia), occupying the caldera of a giant volcano that collapsed on itself after a massive eruption some 100,000 years ago. In comparison, Krakatau's 1883 effort was little more than a belch. The lake is surrounded by steep mountains, ridges and sandy, pine-sheltered beaches.