Lying right in the middle of the province, jewel-like Danau Toba is Southeast Asia's largest freshwater lake, and (at 525m) possibly the world's deepest too. It was formed about eighty thousand years ago by a colossal volcanic eruption: the caldera which was created eventually buckled under the pressure and collapsed in on itself, the high-sided basin that remained filling with water to form the lake. A second, smaller volcanic eruption, 50,000 years after the first, created an island the size of Singapore in the middle of the lake. This island, Samosir , is the cultural and spiritual heartland of the Toba Batak and the favoured destination for foreign travellers. Ferries leave regularly from Parapat - the largest and most convenient gateway for Samosir - and other lakeside towns to the tiny east-coast peninsula of Tuk Tuk and neighbouring Ambarita , the most popular resorts on Samosir. The resorts , with their bookshops, bars and magic mushroom omelettes (illegal but ubiquitous), make Danau Toba the perfect spot to chill out after the rigours of travel in Sumatra. From these resorts you can go trekking in the deforested hills in the centre of Samosir, or cycle around the coastline, calling in at the tiny Batak villages with their flamboyant tombs and distinctive concave-roofed houses.