There are streams flowing under Seoul besides Cheonggyecheon

In the 1960s, Seoul had no sewage system, so they just dumped wastewater into the neighborhood streams. The smell, mosquitoes, and overflowing water when it rained. Streams were a nuisance back then. So, they covered them with concrete. Covering them eliminated the smell and the surface became a road. The problem is that the covered streams became not streams, but massive sewer pipes. However, they couldn't just uncover all of them. Roads and shops were built on top, and even if you dug them up, there was no water inside. The water flowing in Cheonggyecheon now is drawn from the Han River and the subway.