oxygenOn a crisp December morning, office workers and tourists strolled along a tree-lined creek in central Seoul, pausing at the stepping stones that flowed past it. It's hard to imagine that just over 20 years ago, this was a huge elevated highway that carried 168,000 vehicles every day through the heart of the South Korean capital.

Cheonggyecheon, a river that flows about 3.5 miles (nearly 6 kilometers) through Seoul, is one of the earliest experiments in a growing trend in cities around the world: converting spaces that once contained car or rail infrastructure into space for pedestrians and cyclists. It's a powerful example of how these spaces can become beloved and popular, along with projects like New York's High Line, where an old railroad track was transformed into an elevated park, or the moat in Utrecht, One of the multi-lane highways (nicknamed the "highway from scratch") was converted back into a canal as part of a continued push for pedestrians and cyclists to dominate the city center.

The 20th century's rush to build automotive infrastructure has had some terrible consequences, and much to be regretted. Planners on every continent are now taking a hard look at how to relocate people to urban centers.

In Seoul, restored waterways triumphed. Not only does it provide a peaceful refuge from the city’s busy streets, it also serves as a cultural corridor hosting festivals and performances year-round, while helping surrounding communities cool down, combat air pollution and manage increasing monsoon flooding.

"It feels really good here. It's one of the main tourist attractions in Seoul," said Karim, a tourist from Malaysia. In fact, the river's history reflects Seoul's own transformation. It has been an important waterway for the city for more than 600 years, since the Joseon Dynasty (1392-1910), controlling floods and supporting daily life. But by the Japanese colonial period in the 1930s, it had become an open sewer that threatened public health and was called an "urban cancer."

After the Korean War, desperate refugees built shanty towns along the river banks. In the 1960s, Seoul covered it and built an elevated expressway, seen at the time as a symbol of progress and modernity that could mask urban poverty.

By the late 1990s, Seoul was rethinking its development-first ideology. Two devastating infrastructure collapses, the Seongsu Bridge in 1994 and the Sampoyo Department Store in 1995, which killed 32 and 502 people respectively, shook public confidence in the city's aging concrete structures. As citizens began to demand sustainability and a better quality of life, the elevated expressway over the Cheonggyecheon stream required costly repairs or demolition, becoming a test case for new ways of thinking about urban space.

In 2002, Lee Myung-bak won the Seoul mayoral election (and later became president) on a campaign to restore the river. He immediately accelerated the progress of the project after taking office and completed the restoration work in just 27 months at a cost of 386 billion won (approximately 220 million pounds).

"Initially, everyone thought it would cause traffic jams," said Park Byung-chul, a local resident. "But people adapted. Now we can't imagine there ever was a highway here."

According to research by the Seoul Institute, the area around the river is now 3.6 degrees Celsius cooler than nearby streets, creating a cooling corridor in the densely populated center of Seoul. The removal of the elevated highway created new air channels through the city, improving air circulation. Air pollution dropped significantly, with nitrogen dioxide levels falling by 35%.

Wildlife is also back: A 2022 survey by the Seoul Research Institute showed that the area is now home to 666 species, including 174 animal species and 492 plant species.

"This project marks a paradigm shift from vehicle-centered transportation policy to people-centered urban planning," said Minah Park, director of the Cheonggyecheon Stream Museum.

Beneath the natural surface lies complex flood protection infrastructure. The river can handle a 1-in-200-year flood, with special inlets along its course that safely channel monsoon rains through the city center to larger waterways and ultimately to the Han River.

The project was not without criticism or problems. The original stream was seasonal and dried up outside of the rainy season. Today's Cheonggyecheon requires constant maintenance, costing the city 2.9 billion won every year. It needs to pump more than 48,000 tons of water per day (40,000 tons from treated Han River water and 8,300 tons from groundwater) to maintain the flow. Some say this makes it more like an artificial and expensive urban waterway than a truly restored river.

But the project's success sparked wider changes. The city has since demolished 16 other elevated highways, many of which have been replaced with public spaces or wider sidewalks. Cheonggyecheon now attracts more than 12 million visitors a year, making it as central to Seoul life as the city's ancient palaces or bustling markets.

The impact extends far beyond Seoul. "We receive visitors from approximately 30 countries each year through our baseline program," Park said at the museum, noting Tokyo's interest in plans to demolish the Nihonbashi overpass and Nairobi's river improvement project.

As cities around the world grapple with aging highway infrastructure and the need to reduce emissions while adapting to climate change, Cheonggyecheon offers a compelling alternative.