Lambsar, Lamasar, Lambasar, Lambesar or Lomasar was probably the largest and the most fortified of the Ismaili castles. The fortress is located in the central Alburz mountains, south of the Caspian Sea, about 120 km from present-day Tehran, Iran. Lambsar is to the northeast of Razmian village.
Kiya Buzurg Ummid captured the castle from Rasamuj and rebuilt it into a major stronghold using local labour. He was appointed by Hassan-i Sabbah as its governor.Only ruins remain of this magnificent fortress today. Very deep valleys surrounding the fortress make it impossible to access from the East and West sides.