The Imamzadeh Hossein shrine commemorates Hossein, a son of Imam Reza (765-818 AD), the seventh descendant of the prophet Muhammad. The shrine is from the 16th century, the façade dates from the Qajar period.

The guy with the feather-duster is there to wave it at you when your chador is not worn appropriately (and believe me: it's not easy trying to take pictures AND stop the polyester chador from slipping off at the same time!).