Big Ben & Houses of Parliament

Strictly speaking, Big Ben is not a tower. It's not even a clock. Big Ben is the name of the great bell inside Elizabeth Tower — a 13.7-tonne monster that has been booming across Westminster since 1859. The tower was called St Stephen's Tower for over a century and a half before Parliament renamed it Elizabeth Tower in 2012 for the Queen's Diamond Jubilee. Almost nobody calls it that.

The tower rises 96 metres above the Thames, with 334 steps to the belfry and another 65 to the Ayrton Light at the very top — the light that shines whenever Parliament is sitting after dark. The clock itself weighs about five tonnes and is accurate to within two seconds per week, regulated by a stack of old penny coins placed on the pendulum. Adding a penny speeds the clock by 0.4 seconds per day. The four clock faces are each made of 312 sections of opal glass, and the minute hands are 4.3 metres long.

The bell cracked in 1859, just two months after it was installed, which is why Big Ben has that distinctive slightly off-key tone. Rather than replace it, they simply rotated it a quarter turn so the hammer strikes a different spot, and it's been ringing with that signature crack ever since. The bell chimes every hour; four smaller quarter bells mark the quarter hours with a melody based on a phrase from Handel's Messiah.

The Houses of Parliament themselves, officially the Palace of Westminster, were rebuilt in Gothic Revival style by Charles Barry and Augustus Pugin after a catastrophic fire in 1834 destroyed most of the medieval palace. Only Westminster Hall survived — its magnificent hammerbeam roof, dating from 1399, remains one of the largest medieval timber roofs in Europe. The palace contains around 1,100 rooms, 100 staircases, and over three miles of corridors.