Karlstein am Main (officially "Karlstein a. Main") is a municipality in the Aschaffenburg district in the "Regierungsbezirk" of Lower Franconia ("Unterfranken") in Bavaria, Germany. It is the westernmost settlement in Bavaria. Karlstein's "Ortsteile" (constituent villages) 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