Mentioned by Devon 21 days itinerary
See the Best of England: A Three Week Itinerary
"Westminster Abbey – This large, mostly Gothic, church is one of the most notable religious buildings in the UK and is the traditional place of coronation and burial site for British monarchs. It is simply breathtaking both inside and out but it is inside that you will find so much to explore. Make sure you allow a good few hours to visit properly."