THERE'S a place in Seoul to which many of its denizens escape when the snarling traffic and jostling crowds get too overwhelming.

Here, they soothe their jangled nerves by dipping their bare feet in a gurgling stream and watching birds play among river reeds.

They don't have to travel far. In fact, the Cheonggyecheon is just a hop and a skip away.

A 6.8km rivulet with a riverbank area which cuts through the heart of the city, this green lung is not just an ecological attraction. It is also a recreational and cultural bait, with sculptures, fountains, historic bridges and waterfront decks dotting various stretches.

It wasn't always this way. For nearly half a century until 2003, the stream was covered by a four-lane, two-way highway used daily by 170,000 vehicles.

The Cheonggyecheon's historical significance dates back 600 years, when Seoul became the capital of the Joseun dynasty in 1392.

Running from west to east, it not only divided the capital geographically but was also a political, cultural and social boundary. People from the upper classes, for instance, lived in the north; the poor congregated in the south.

Sanitation, however, became a big problem because the little river served so many functions. This was especially acute during the Japanese Occupation from 1910 to 1945, when poor farmers from all over the country set up home along its banks. The place became one big shanty town. And 'clear valley stream' - as the Cheongyecheon is known in Korean - had become a sewer.

In 1958, work to conceal the eyesore began. It became a road which in turn became a 16m-wide highway in 1976.

However, the expressway soon became a public hazard. It began to groan under the sheer volume of vehicles it bore.

The structural decay was made worse by carbon monoxide, methane and other gases underground. Although strengthening work on the highway was done periodically, structural engineers recommended tearing it down in the interests of public safety.

In 2002, then-mayor Lee Myung Bak announced that the highway would go, the river would be restored and a 400ha park created alongside it.

The project cost an estimated US$386 million and was as ambitious as it was meticulous.

Demolition work started in July 2003. Diamond-wire and wheel saws - the most advanced technology available - were used to methodically slice up the highway and minimise noise, dust and other pollution for the area's commercial and residential buildings. The highway was completely dismantled about a year later.

Intercept sewers were constructed to get rid of the filth.

The restoration was a marriage of technology and creativity.

Among other things, 120,000 tonnes of water gets pumped every day from the city's Han River and subway stations to make sure the river always gurgles. Embankments were built to withstand the worst possible floods. Sculptures, fountains and murals also dot the riverbanks while long-buried bridges and foundation stones were restored and reinstated.

Local newspapers dubbed the scheme 'the greatest urban renewal project in modern Seoul history'.

In October 2005, the restored river project opened.

The effects were remarkable in more ways than imagined.

Fish and birds started migrating to this sanctuary, thanks to the biotopes (spaces with uniform environmental conditions) introduced throughout the waterway.

The stream has become almost like an air cooler and purifier throughout the city, credited with reducing the temperature of the surrounding area by between 2 deg C and 3 deg C.

The value of nearby land and apartments reportedly shot up by over 40 per cent. Cafes, restaurants and other lifestyle businesses mushroomed.

In the first 16 months after its restoration, more than 40 million people visited the river, drawn by attractions such as the 22 historical bridges, nine fountains, Sky Water Site and the Willow Swamp. There is even a Cheonggyecheon Museum, which chronicles the history of the river.

At Cheonggye Plaza - where the Cheonggyecheon begins - crowds throng cheek by jowl to see the tri-coloured fountain and a beautifully lit waterfall cascading four metres.

This is said to have become one of the most popular spots in Seoul for men to propose to their girlfriends.

Overseas Korean Marion Pak, who has lived in Los Angeles for 22 years, was pleasantly surprised by the makeover when she returned on a visit.

'When I was growing up, it was a dirty and contaminated river,' the sixty-something housewife told The Straits Times. 'Like many Koreans overseas, I had heard how they restored the river and I came back to see it. Now I can see clear water and fishes swimming. I am very happy and very proud.'

That same pride was echoed by teacher Kim Yeon Kyung, 32.

She strolls along the river with her mother and her baby son at least once a fortnight.

'It's amazing that we have a stream in the heart of the city. I remember the highway and how it was so dirty and crowded. Now it's so modern and so fresh. Instead of cars, you see green. Instead of traffic, you hear water.'

To Ms Kim, the river is almost a symbol for Seoul.

'It's made the city so alive.'

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» Singapore: City of green gardens and blue water
» From blight to beauty - Seoul's way