Tokyo is home to the world’s tallest tower, Tokyo Skytree, and the world’s largest underground floodwater diversion facility, the Metropolitan Area Outer Underground Discharge Channel (located in Kasukabe, Saitama, a suburb of Tokyo). The Tokyo Metro Ginza Line, opened in 1927, is the oldest underground metro line in East Asia. Recognized as one of the most livable cities in the world, Tokyo was tied fourth with Wellington in the 2021 Global Livability Ranking.