Cheonggyecheon is a small stream that once flowed from a cirque of mountains that surround the historic center of Seoul into the Han River, 6 kilometers away.
In the years immediately following the Korean War, Cheonggyecheon was overrun by informal refugee camps, shantytowns, and sewage. The stream was soon paved over for a wide boulevard; in 1968, during Korea's own urban renewal fad, an elevated highway was stacked above the road. In spite of its historic and cultural significance to Korea, Cheonggyecheon spent over half a century in an underground culvert, choked with filth.
Then, in 2003, in an act of political will that seems miraculous to me, Seoul mayor Lee Myung-bak began a project to remove 16 lanes of stacked expressway and restore the lost stream beneath. Two years later, a vibrant, wild park had replaced a traffic-choked freeway. Believe it or not, the two photos above show the same section of stream (the two buildings in the center-right of the top photo, taken sometime early in the 2000s, are the same two buildings on the left side of the bottom photo).
Tearing out a huge downtown freeway didn't create mass gridlock, as the project's opponents had promised: traffic actually moves faster and more smoothly today than it did when the freeway was there. In an interview with the Guardian two years ago, Kee Yeon Hwang, a professor of urban planning, said that "as soon as we destroyed the road, the cars just disappeared and drivers changed their habits. A lot of people just gave up their cars. Others found a different way of driving. In some cases, they kept using their cars but changed their routes." In other words, people aren't as stupid as traffic engineers think they are. Koreans gave the project a definitive seal of approval when they gave Lee Myung-bak, the project's primary political champion, a promotion to the presidency in 2007.
By replacing idling cars with a naturalized waterway, Seoul also lowered summer temperatures in the center of the city and improved air quality and circulation. The Cheonggyecheon isn't yet a functioning watershed: the water flowing from the "headwaters" in the center of Seoul is currently being pumped uphill from the Han, instead of trickling down from the mountains. But it's still attracting wildlife, including fish and herons, and there are more plans in the works to restore elements of the stream's natural hydrology.
Of all the parts of the park I've looked at, this one's my favorite: three remnant highway abutments standing in the middle of the stream like a utopian apocalypse scene - a glimmer of hope that the brutal regime of freeways and highway engineering is losing its grip on the world's cities. Credit for the photo goes to Flickr user Ben Harris-Roxas: