The Tower of London, built by William the Conqueror after the Norman Conquest. Survived the next 900 years as palace, prison, royal mint + execution yard. The White Tower is the oldest part of the site, begun by William + completed by Henry III.
Pie and Mash shops unique to the UK, Lovely meat pies with mashed potatoes and green (parsley) Liquor. I have had it delivered from this shop Manze, they deliver all over the UK and it's the original thing. Pie and Mash shops also serve Jellied Eels