Big O is a centerless Ferris wheel in Tokyo Dome City. It was the first centerless Ferris wheel in history and, as of 2006, the largest one in the world at 60 metres (200 ft) in diameter. Tokyo's largest roller coaster, the 130 kilometres per hour (81 mph) Thunder Dolphin, passes through the centre of the wheel.
Tokyo Dome City Attractions (東京ドームシティアトラクションズ) is an amusement park located next to the Tokyo Dome in Bunkyō, Tokyo, Japan, and forms a part of the Tokyo Dome City entertainment complex. It opened in 1958, and was formerly known as Kōrakuen (後楽園ゆうえんち) until April 2003. It was one of the most popular amusement parks in Tokyo. Rides include the Big O Ferris wheel and Thunder Dolphin roller coaster.