The imambara in Lucknow is popularly called the 'Bara Imambara' This majestic imambara built by Asaf-ud-Daula in 1784 is also called the 'Asafi Imambara'. The imambara is a shrine built by Shia Muslims to observe Azadari. Azadari is the mourning of Muharram which takes place in the first month of the Islamic Calendar.
The legend behind the imambara is that there are many hidden passageways that lead one to a location near the Gomti River, to Faizabad, the former seat of power of the Nawabs or they may lead to Allahabad and Delhi. After a period of long disuse, they were sealed as there were reports of many people going missing while exploring these passageways of the Bara Imambara.
The Mughal Architectural sytle imambara was built during a time of intense famine and Asaf-Ud-Daula started this project to provide employment for people in the region battling with the famine. This work lasted for a period of 10 years. The design does not incorporate any European elements or the use of iron.
While in Lucknow, this is a grand complex that should surely make it to your list of 'places to see in Lucknow'.