Also old: Westminster hall (https://en.wikipedia.org/wiki/Palace_of_Westminster#Westminster_Hall https://en.wikipedia.org/wiki/Palace_of_Westminster#Westmins...

Also old: Westminster hall (https://en.wikipedia.org/wiki/Palace_of_Westminster#Westminster_Hall https://en.wikipedia.org/wiki/Palace_of_Westminster#Westmins...), built in 1097 and still in active use today. I could care less for the rest of the Palace of Westminster, but the hall is absolutely stunning. The best way to see the hall is to attend a public meeting hosted in parliament as it will be free.