The Shrine of Imam Reza in Iran's Mashhad is one of the largest mosque complexes in the world - spoken of in the same breath as those in Mecca and Medina - and reportedly counted Guru Nanak, the founder of Sikhism, as one among the millions who have visited it over the years.
It feeds over 10,000 devotees daily, hosts weddings, and its 2.5 lakh sq km contains a fully-equipped hospital, a library and a museum, as well as the mausoleum of Imam Reza, the eighth Imam, who is from the lineage of Hazrat Ali and Fatima Zahra - the daughter of the Prophet Mohammed
Around three crore people from all around the world, including India, visit his grave every year. According to Hussain Yazdinizad, a shrine committee member, this includes people from other faiths. "There are arrangements for those who do not know Persian... for them we have kept translators who speak different languages and can tell them about the mosque," he said.
An organisation called Astan-e-Quds Razavi manages the shrine; the committee is the oldest such Iran and counts around 20,000 volunteers from businessmen to college professors, who do everything from welcoming visitors and pick up their shoes to serve them tea.
The shrine also boasts a copy of the Dome of the Rock, made in memory of the Al Aqsa Mosque, which is in Jerusalem. Here, the people of Iran stand with those of Palestine - a significant fact given the current geopolitical tension in the Middle East.
According to Shia history, there were 12 Imams after the Prophet. The first was Hazrat Ali and the eighth was Ali Reza. The 12th and final was Hazrat Mehdi, who tradition says is still alive and will come into the world just before the apocalypse.
The graves of 10 of the Imams are either in Iraq or Saudi Arabia; that of Ali Reza is the only one in Iran. The shrine of his sister, Fatima Masooma-e-Qum, is also in Iran, in Qum.