The Tower of London was a London landmark founded by William the Conqueror in 1078.
History
Henry VIII once sent the First Doctor to the Tower of London, which is where the Doctor wanted to be as that's where his TARDIS had also been taken. (DW: The Sensorites)
The Doctor was later imprisoned in the Tower of London again, where he shared a cell with Sir Walter Raleigh. (DW: The Mind of Evil)
The First Doctor assisted Lady Jane Grey and was present at her execution at the Tower. (VD: The Nine-Day Queen)
The Doctor would end up there yet again, this time with Nyssa, after running afoul of Sir Isaac Newton. (BFA: Circular Time)
In 2006, UNIT headquarters was located beneath the Tower of London. (DW: The Christmas Invasion) The headquarters was still used in 2009, though UNIT also maintained mobile bases in lorry trucks. (DW: The Sontaran Stratagem)
When The Department controlled Britain around the year 2050, the Tower of London became Dauntless Prison, a prison for all the aliens that arrived on Earth. When K9 Mark 2 and his friends released the alien prisoners there in 2050, the Department's treatment of the prisoners was leaked to the media and the prison was shut down. (K9TV: Liberation)
Sometime around the 29th century onwards, the tower was incorporated into Starship UK, its dungeon containing the devices used to torture the Star Whale beneath the craft into moving. (DW: The Beast Below)
