Cheonggyecheon is a 10.9-kilometre-long (6.8 mi) stream and public space in downtown Seoul, South Korea. A natural stream sourced from the Suseongdong Valley in Inwangsan, it was historically maintained as part of Seoul's early sewerage until the mid-20th century, when post-Korean War rapid economic development and deteriorating conditions prompted the filling of the stream with concrete and the construction of an elevated freeway, the Cheonggye Expressway, in its place. In 2003, the city government began an urban renewal project to remove the expressway and restore the stream, which was completed in 2005 at a cost of over ₩386 billion.