Karlstein am Main is a municipality in the Aschaffenburg district in the Regierungsbezirk of Lower Franconia in Bavaria, Germany. It is the westernmost settlement in Bavaria. Karlstein's Ortsteile are Dettingen and Großwelzheim, the former being notable as the site of the Battle of Dettingen during the War of the Austrian Succession. In the 20th century, the town was the site of the, now decommissioned, Großwelzheim Nuclear Power Plant