Chand Baori stepwell, located near Jaipur in Rajastan, India. These 20 meter deep stepwells descending 11 flights built in the 10th century, were used to reach the groundwater, as a place to escape the midday heat and for social gatherings.
Additional information:
http://en.wikipedia.org/wiki/Chand_Baori
A youtube video:
http://www.youtube.com/watch?v=wFYaWVXOu5E
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