The O2 is a large entertainment venue located in Greenwich, London, originally built as the Millennium Dome in 1999. It was transformed into an arena in 2007 and has since hosted a variety of events, including concerts, sports, and exhibitions. The venue has a seating capacity of up to 20,000, making it one of the largest indoor arenas in the UK. In addition to the main arena, The O2 complex includes a cinema, restaurants, and bars, providing a complete entertainment experience. It is also home to the O2 Academy, which hosts smaller live music events. The O2 is easily accessible via public transport, making it a popular destination for both locals and tourists.