At the edge of town is Gonbad-e Jabaliye, an octagonal and very old structure of unknown provenance. Some scholars date it to the 2nd century AD and think it may have been an observatory. Others say it was a tomb. Whatever its function, it is remarkable because it is constructed of stone rather than the usual brick; though the double-layered dome, added 150 years ago, is brick. Today it houses a museum of old gravestones. Be careful not to photograph the neighbouring army base.