Vättern is the second largest lake in Sweden, being about 135 km long and up to 31 km wide. It has a total area of 1 912 km2. The depth at the deepest point is 130 m.
Vättern is located between the cities of Jönköping and Askersund. Göta kanal connects the lake with Östersjön in the east and Vänern in the west.
Before the 18th century all attempts at measuring the depth of the lake were futile, and people actually believed the lake was bottomless, and connected to other lakes via underground rivers. One lake Vättern was believed to be connected to is Lake Boden in the Alps. Myth has it that the body of a woman drowned in Vättern was found in that specific lake.