This riverwalk used to be a famous river, then was covered over before WWII, then became a sewer, then they built an elevated highway on top of that. The current president was then the mayor of Seoul and had a crazy idea to tear down the busiest highway in a city of 20 million plus and divert a sewer, and make the old river into a family park. It worked and is remarkably popular for a former river/sewer/highway.