The Cheonggyecheon Restoration Project (2003-5) was an ambitious urban initiative to restore a 5.8-kilometer stream in central Seoul by demolishing elevated highways and peeling back the decades-old concrete pavement. A massive civil engineering project in itself, the restoration work caused heated debates on whether it brought back "an environmentally friendly civic jewel'' or resulted in a humongous "fish tank'' with an artificial water supply and meticulously engineered vista. This article examines the design, implementation, and critique of the restoration project by taking an envirotechnical position that restoration is fundamentally about negotiating nature, technology, and history. First, the designers and engineers struggled to determine how much nature and how much technology should constitute the new Cheonggyecheon so that it could recover its original state. Second, planners and officials deliberated which parts of the city's past the restoration should reference and display. It turned out that a distant, dynastic era was brought back while a recent, contested history of rushed industrialization was pushed away, both physically and symbolically. Even as the critics of the restoration project pushed for a new "re-restoration'' project, the central dilemma of finding the right reference for restoration remained unresolved. The Cheonggyecheon project shows that restoration is a never-ending effort that mobilizes what is available at the moment in the repository of nature, technology, and history.