It is a long, finger-shaped body of fresh water in south central Sweden, to the southeast of Vänern, pointing at the tip of Scandinavia.

Being a deep lake at 128 metres (420 ft) below sea level at its deepest point, Vättern is about 1/3 the surface area of Vänern but in contains roughly 1/2 of its volume of water.

Vättern drains into Motala ström through Bråviken into the Baltic Sea, but also has a downstream connection since 1832 through the Göta Canal to Vänern and the Kattegat tributary of the Atlantic Ocean.

[9] During the most recent millions of years multiple glaciations have covered the lake and its surroundings, leaving glacial striations and drumlins as they receded.

The present-day lake began as an independent body of water left by the receding Scandinavian glacier after the last glacial period around 10,000 BP.

Subsequently, it was a bay of Yoldia Sea and then became connected to Ancylus Lake, discharging from the north end of its extent.

At about 8000 BP an accident of the uneven Scandinavian isostatic land rise brought Vättern above Ancylus and the two became distinct.

Vättern is known for the annual recreational cycling race Vätternrundan, attracting some 20,000 participants to finish the 300 km trip around the shores of the lake.

According to the Catholic Church, Saint Catherine of Vadstena performed a miracle involving three people in peril on lake ice.

All the inhabitants round about it are deafened with the hideous roaring of his waters when the winter breaketh up, and the ice in his dissolving gives a terrible crack like to thunder, whenas out of the midst of it, as out of Mont-Gibell, a sulphureous stinking smoke issues, that wellnigh poisons the whole country.

John Bauer, his wife Ester and their three-year-old son, Bengt, drowned in the sinking in bad weather of the steamer Per Brahe on the lake on the night 19 November 1918.