Since 1549, the cathedral has had the tallest church spire in the United Kingdom, at 404 feet (123 m). Visitors can take the "Tower Tour" where the interior of the hollow spire, with its ancient wooden scaffolding, can be viewed. The cathedral also has the largest cloister and the largest cathedral close in Britain at 80 acres. It contains a clock which is among the oldest working clocks in the world and has the best surviving of the four original copies of Magna Carta. In 2008, the cathedral celebrated the 750th anniversary of its consecration.