In north of Kashan,there is a small town called Nooshabad . Despite its remarkable scale , it was unknown until decades ago . This underground city is the largest underground city in the world . Nooshabad underground City was built 1500 years ago, by order Sassanid king . Three floors were built with strange Halls , food storages , water , Fat-burning lights and even toilets for long time residence of local people for protection against foes and invaders. Ouyi City or Nooshabad Underground City is built under ancient part of Kashan City and is extended even under the present city site . The city was accidentally discovered by the man who digs the yard . This Amazing city with its surprising road map is one of the Adventure Attractions In Iran .