The document provides several facts about Big Ben and the clock tower in London: - Big Ben is the nickname of the largest bell in the clock tower at the Houses of Parliament in London, though the tower itself is officially called the Elizabeth Tower. - The four clock faces are over 7 meters in diameter and are cleaned every 5 years by workers who abseil down the tower. - The tower leans slightly to the northwest due to changes in the ground since it was built over 150 years ago.