On more than 80 kilometres in length, a natural river will return in the middle of Europe's largest conurbation, which has existed for 100 years as an open sewer. The largest Deep Gravity Sewer Tunnel in Europe enables this transformation process. With total depths up to 40 below ground the Emscher Sewer is an extreme challenging pipe jacking project. The new pipeline, which begins in Dortmund just below the sewage treatment plant of Dortmund-Deusen, will run to the sewage treatment plant “Emscher Mündung” in Dinslaken. Because of the fact that the pipeline will be filled permanently with sewage new, state-of-the-art inspections concepts, based on roboter technology were developed to enable operation and maintenance. The paper gives an overview of the project, starting from the approval process, to the final design up to the construction and monitoring.