Iran ancient underground power plants, Kariz

A Qanat Qanat is one of a series of well-like vertical shafts, connected by gently sloping tunnels. They create a reliable supply of water for human settlements and irrigation in hot, arid and semi-arid climates. The qanat technology is known to have been developed by the Persian people sometime in the early 1st millennium BC and spread from there slowly to the west and east.