Millennium Dome. Night-time view of the Millennium (or Greenwich) Dome in London, England, with the River Thames in the foreground. It is the largest dome in the world and will contain the Millennium Experience, a huge exhibition to celebrate the arrival of the year 2000. The exhibition has 14 themed zones dealing with topics like play, faith, business and the body. The 2 mm thick roof, made of teflon-coated glass fibre fabric, is supported by 70 km of steel cables attached to twelve 100 metre high masts. Rainwater falling onto the roof will be collected, filtered and stored, ready for use in the Dome's toilets. The Dome is 320 metres across and will hold over 40,000 visitors.