The O2 and the Indigo2 are London's most popular music-orientated venues, based in perhaps one of London's busiest hubs. The 20,000 capacity O2 is Europe's busiest arena as well as it's second largest (dwarfed only by the Manchester Arena), and plays host to almost every big name when they head to the UK, while its 3,000 capacity sister Indigo2 acts as more of a super club. Between them, they attract millions upon millions of fans year in year out.