Bad Karlshafen is a baroque, thermal salt spa town in the district of Kassel, in Hesse, Germany. It has 2300 inhabitants in the main ward of Bad Karlshafen, and a further 1900 in the medieval village of Helmarshausen. It is situated at the confluence of the Diemel and Weser rivers, 15km south of Höxter, and 37km north of Kassel.