Lake Toba (Danau Toba), on the island of Sumatra in Indonesia, is the largest volcanic lake in the world. Samosir island, in the lake, is an island within an island. It is located at North Sumatra.
Lake Toba is an immense volcanic lake covering an area of 1,707 km2 (1,000 km2 bigger than Singapore) with an island in the center. Formed by a gigantic volcanic eruption some 70,000 years ago, it is probably the largest resurgent caldera on Earth. Some studies say it might have been associated with causing previous ice age/climate change and the largest human population bottleneck ever.
Lake Toba was perhaps once more popular than it is nowadays, but for many it remains a firm fixture on the Banana Pancake Trail. It is a great laid back place to chill out for a few days after jungle trekking etc. The location is very popular with Chinese tourists around Chinese New Year, when availability drops dramatically and accommodation costs skyrocket. In its effort to promote tourism, government has greatly improved the infrastructure.