The Tower of London was a London landmark founded by William the Conqueror in 1078.
History
Henry VIII once sent the 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 Doctor assisted Lady Jane Grey and was present at her execution at the Tower (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)
