Facing St. Bart's Hospital from Smithfield Market, you will see an innocuous looking arched doorway on your left.
It's the entrance to the courtyard for St. Bartholomew the Great church, founded in 1123, making it the oldest church in London (they claim). I shared the entire sanctuary with one other person (an employee).
The church has appeared in several movies, including Four Weddings and a Funeral, Shakespeare in Love, Amazing Grace, Elizabeth: The Golden Age and The Other Boleyn Girl.
London trip report: http://bit.ly/1gZcVuX