Agrasen ki Baoli is a 60-meter long and 15-meter wide historical step well — reservoir for water — in New Delhi, India.
The water was falling down step by step and people could collect it the main storage down the stairs. During monsoon the level of water increase, covering the half of the hight.
Unfortunately, nowadays stepwells are not used. The authorities during the British Raj found the hygiene of the stepwells less than desirable and had installed pipe and pump systems to replace their purpose.
The importance of water to the locations in which they were found have been realized in recent decades, now that many communities in the area have scarcity of rain and water. The construction of these wells encouraged the incorporation of water into the culture where they were popular. These stepwells were proven to be well-built sturdy structures, after withstanding earthquakes in the range of 7.6 on the Richter scale.
Information is taken from Wikipedia for general overview.