Lambsar (, also pronounced Lamsar), Lambasar, or Lambesar was probably the largest and the most fortified castles of the Nizari Ismaili state. The fortress is located in the central Alburz mountains, south of the Caspian Sea, about 120 km from present-day Tehran, Iran. Lambesar is to the northeast of Razmian village (the central district of Roodbar e Shahrestan).