34.2900°N, 58.6544°E.
The Gonabad Qanat (Qasabeh) in Razavi Khorasan Province, northeastern Iran, is the oldest and largest known qanat in the world, with construction conventionally dated to the late 1st millennium BCE and possibly Achaemenid in origin under the reign of Cambyses or Darius I. Its mother well descends some 280 to 300 metres into an alluvial fan beneath the Siah Kuh range — a vertical shaft so deep that the loss of even a single workman during construction was a routine risk recorded in local oral history. The main gallery runs roughly 33 kilometres to surface inside the city of Gonabad, with more than 470 vertical access and ventilation shafts along its length, all dug entirely by hand without machinery, ventilation fans, or electric light. The system still irrigates fields and supplies drinking water to thousands of people, and was inscribed by UNESCO in 2016 as part of the Persian Qanat serial property.
The Gonabad Qanat (Qasabeh) is a 2,500-year-old underground river maintained, generation after generation, by men who crawl in to clear it by candlelight.