Palace of Westminster

Start here, because everything else on this list orbits it. Sitting in the public galleries of the Commons or the Lords to watch a debate costs nothing, and seeing ministers answer questions face to face shows how accountable British government is meant to be. The guided tour is the way to see the rest, including Westminster Hall, built for William II in 1097-99 and the room where Charles I was tried. UK residents can ask their MP for a free tour; everyone else books a paid one, offered on Saturdays and on many weekdays when Parliament is in recess. The Elizabeth Tower climb to Big Ben is 334 steps, for ages 11 and up, with tickets released on the second Wednesday of each month at 10:00.