What used to be a small stream that flowed through the downtown area was hidden beneath a truck bypass for decades. In 2003, the mayor of the city decided to restore the stream and give the city some much-needed natural space -- the bypass was removed, walking paths were opened, and 22 bridges were built. The stream now covers an area 11km (6 3/4 miles) long and its revival is one of the best things to happen to the city in the past few years. Night or day, it's a great place to take a stroll, as Seoul's skyscrapers loom on either side of you.
The city offers two different walking tours of Cheonggyecheon, each guided by a cultural heritage commentator, three times a day. The free tours take about 2 to 3 hours and you need to make a reservation at least 3 days in advance.
Bus tours of Cheonggyecheon are also offered, departing from in front of Gwanghwamun Donghwa Duty Free Shop (subway line 5 to Gwanghwamun Station, exit 6). The tour takes up to 2 hours (depending on traffic) and departs at 10am, noon, 2pm, 4pm, and 7pm. Call the Gwanghwamun Tourist Info Center to make reservations. There are no tours on Mondays, except when it's a holiday.