Gonabad Qanat (aqueduct) is one of the greatest and deepest hydraulic systems in the world. It is located in Khorasan province, at the heights of Siahkooh, in the southwest of Gonabad city.
It reflects the 2500 years historical background of Achaemenid period in Khorasan. According to the latest studies this Qanat is 33113 meters in length, it has more than 470 wells and the depth of the main well is about 280 to 300 meters. These wells have been built based on different sciences such as physics, hydraulics and geology that made it possible for the residents to live in such a dry land with low rainfall.
It is comprised of a main branch and 6 tributary branches. The oldest water clocks in the world have been used as a practical application in Zeybad and Gonabad Qanats.they were used as practical ancient tools to time the yearly calendar of Iran.