Langsee or Längsee may refer to: Längsee (Kärnten), a lake of Carinthia, Austria Längsee (Tyrol), a lake of Tyrol, Austria Langsee (Schleswig), a lake in Angeln, Kreis Schleswig-Flensburg, Schleswig-Holstein, Germany Langsee (Mecklenburg), a lake in the Rostock district in Mecklenburg-Vorpommern, Germany