The Tower of London, United Kingdom is a fortification in the center of the city. It contains a castle surrounded by two walls and it has been used over the centuries as a royal safe-harbour, prison, zoo, museum and armoury. It has been built in the 11th century CE for William the Conquerer and is a UNESCO World Heritage site since 1988.
Today it is a museum exhibiting weaponry and the crown jewels. The list of of imprisoned kings here is pretty long and there are different stories about their stays. One of the last prisoners was Rudolf Heß, a Nazi leader. Beware of the ravens in the Tower, they are important: it is said that when they leave this place, the Empire will fall.
Tower of London
London EC3N 4AB