To fully comprehend what a mammoth and expensive effort it was to resurrect Cheong-gye-cheon, Seoul’s long buried east–west stream, pay a visit to this excellent museum. It's also a good starting point for a walk along the revitalised waterway – 2.5km west to Dongdaemun Market. Don't miss the Cheong-gye-cheon Cardboard House museum opposite, a wooden shack typical of the slum housing that sprawled along the stream after the Korean War.