Noosh Abad underground city known as "Ouei" and the largest underground city of the world, with human made architecture constructed on three floors with the military and defense applications.
The dating of this great complex backed to Sasanian and early Islamic eras and it was used in Seljuk and Safavid and even in Qajar era. This underground city has been formed in order to protect the residents against the onslaught of the enemy in the old area of the city and has been extended to the current level. The entrances of this complex have been created in different ways and in hidden forms by a well or a narrow and short channel in the house or inside the adobe castle beside the city, crowded districts such as Bazaar, inside the riffles (access place of water aqueduct) that was made under the houses, the wells inside the mosque, gardens or wherever the possibility of escape and quick access in case of enemy's attack provided.
These related wells to floors, in addition to the traffic had been used in order of air conditioning on the below floor. Except for the main entrance, the height of the other parts of Ouei is about normal height of human between 170 to180 cm. The interior of this place consists of several rooms which are connected to each other by narrow and specific corridors. Also, in this complex, restrooms, place of the oil lamp and short platforms have been created in the wall. This place has also a structure for trapping the enemy in case of entering the shelter. No mortar used in the construction of this complex.