One of Britain's most famous tourist attractions. Big Ben started working in May 1859. The name "Big Ben" is actually the name of the giant bell in the belfry of the clock tower. The bell weighs nearly 14 tons. The bell is struck by a hammer from the outside. The clock's official name is 'The Great Westminster Clock'. It is accurate within one second. The clock tower is 316ft high. The tower has no elevator, there are 334 limestone steps to the top.