The ruined monument which appears as a tall tower to the north of the palace area is known under the name of Zendan-e Soleyman or the ("Prison of Solomon"). The monument is severely damaged, and its study relies largely on the very similar building called the Ka'beh Zardusht at Naqsh-e Rostam. The Zendan rises to a height of 14 m, and consisted of a square stone tower capped with a pyramidal roof, which was buttressed at the corners with three rows of false windows on three sides of the building in a manner that is very similar to the design of the better preserved Ka'beh Zardusht.
It seems now necessary that a thorough reinvestigation and restoration work be carried out at the Zendan with the objective of the permanent consolidation of the monument, and its scientific restoration that may fulfill a double-goal: a better understanding of the monuments and its different architectural features; the appropriate restoration of the edifice. The initial step was taken during two seasons in the summer and autumn 2006. A second season of work is now scheduled for the fall 2009.
Recent archaeological investigations at the site show that this enigmatic monument can be better understood in its full archaeological context. The surroundings of the building are dotted with a number of features and structures, the exploration of which will reveal significant evidence that may elucidate questions regarding the function of the monument.