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 in the year 2000 will contain the Millennium Experience, a huge exhibition to celebrate the millennium. The exhibition has 14 themed zones on topics like business, faith 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 for use in the Dome's toilets. The Dome is 320 metres across and can hold 40,000 visitors.