How heavy is the Big Ben bell? It weighs 13.5 tons. How tall is the Burj Khalifa in Dubai? 829.84 metres from top to bottom. How big is Buckingham Palace? It's got 775 rooms. How long is the Great Wall of China? Experts say about 5,500 miles (8,850km). How wide is the Grand Canyon in Arizona? It varies from 4 to 13 miles across (6.4-21km) How old is Angkor Wat in Cambodia? Approximately 1,000 years.