The Chapel of St John is the oldest church in London and situated in the Tower of London on the second floor of the White Tower.
The Tower of London was built in 1077 - 97 by William the Conqueror.
A door from the Great Chamber on the second floor leads to the north aisle of the Chapel of St John the Evangelist.
A gruesome discovery was made under the stairs leading to the chapel. The remains of the bodies of the two Little Princes, Edward V and his younger brother Richard, Duke of York were found who were reputedly killed on the orders of their uncle the Duke of Gloucester, afterwards Richard III (although some scholars name Henry VII as the culprit).
The Tower of London was used as a prison for many years and the "Pokers and Tongs" refer to the instruments of torture which were used there!
We recommend castles.me.uk for fully comprehensive details regarding the Tower of London.