Khettara shaft, Moroccan desert. Stone walls of a shaft for an ancient underground network of water transport tunnels called khettaras. These tunnels are used to transport water from an aquifer or oasis to human settlements. Many khettaras (also called qanats) are hundreds of years old and are no longer maintained, but some are being restored. The access and air shafts, some many metres deep, need to be cleared and reopened to allow them to be used to supply air and to descend to the tunnels to carry out maintenance.