St Mary Moorfields is a Roman Catholic church in Eldon Street near Moorgate, on a site previously known as Moorfields. It is the only Catholic church in the City of London. Prior to 1994, the church was designated as being in the Borough of Hackney, such that there were no Catholic churches in the City. Wikipedia
Often open but often in use. Very popular for weddings. Worth getting in contact before visiting.
Nearest stations: Liverpool St. and Moorgate.
City of London Churches 