The hexagonal Ziggurat of the Kolahfarangi or Mir Hassan Khan Castle is a unique landmark of Birjand. This building was originally the residence of Hassam-al-Dowleh but dates to the Zand Dynasty. This building is six stories high and only two floors are practically usable. The interior and exterior decorations are honeycomb plasterwork, flowerpot motifs and niches, are major decorations on this building. The forms and shapes of this building makes it one of the unique buildings of Iran.