In Seoul, the water of The Cheonggye stream became progressively more polluted and in the 1970’s the river bed was turned into a road, then an elevated six-lane motorway was built above it.
In 2005, after 6 years of planning, the road and the stacked expressway was removed. Now a park has replaced the freeway and the water in the river is restored, albeit mainly from groundwater.
Three broken highway abutments have been preserved to memorialize the demolished expressway, “we have to give our education to our descendants not to make the same mistake twice”.
An interesting interview of Kee Yeon Hwang, urban planner and designer, principal author of the masterplan, in the Guardian