Imam Reza Shrine in Mashhad, Iran is a complex which contains the mausoleum of Imām Ridha, the eighth Imam of Twelver Shi’ites and known

Imam-Reza-Shrine

as third largest mosque of the world. Also contained within the complex include: the Goharshad Mosque, a museum, a library, four seminaries, a cemetery, the Razavi University of Islamic Sciences, a dining hall for pilgrims, vast prayer halls, and other buildings.

source : http://thewondrous.com