The Millennium Dome was the name of a dome-shaped structure located on the Greenwich Peninsula, in London; and built to hold an exhibition honoring the down of the 3rd millennium; the event was open to the public from January 1st to December 31st of 2000.
The structure has 365 meters in diameter (1 m for each day in a year) and a circumference of 1 Km.
The Dome is now known as the O2 arena.