World's Biggest Clock In Mecca - Saudi Arabia is going to introduce the world's biggest clock sits 400 meters up and that will also be the world's second-tallest skyscraper and largest hotel, overlooking the city's Holy Grand Mosque, which Muslims around the world turn to five times a day for prayer. Local media have said that the clock tower project cost $80 crores. It has four faces measuring 43 meters in diameter.