Lake Toba is a large natural lake in North Sumatra, Indonesia, occupying the caldera of a supervolcano. The lake is located in the middle of the northern part of the island of Sumatra, with a surface elevation of about 900 metres (2,953 ft), the lake stretches from 2.88°N 98.52°E to 2.35°N 99.1°E. The lake is about 100 kilometres long, 30 kilometres (19 mi) wide, and up to 505 metres (1,657 ft) deep. It is the largest lake in Indonesia and the largest volcanic lake in the world. Toba Caldera is one of twenty geoparks in Indonesia, and was recognised in July 2020 as one of the UNESCO Global Geoparks.

Toba Batak is an Austronesian language spoken in North Sumatra province in Indonesia. It is part of a group of languages called Batak. There are approximately 1,610,000 Toba Batak speakers, living to the east, west and south of Lake Toba. Historically it was written using the Batak script, but the Latin script is now used for most writing.