Tower of London

It is the Queen’s royal palace and fortress, which is considered a historic castle alongside River Thames. It was founded in 1066 when the Normans conquered England and was considered a symbol of oppression by the rulers. Although made as a royal residence initially, it was used as a prison shortly after its establishment, which gave it the notoriety. Since the World War II, it has become a tourist spot protected under the World Heritage Site. [Source]