The Sewerage Museum in Paris, as early as 721 in Beijing, heard that "Sewerage is the conscience of a city". These channels lead to the Seine River, which is usually closed. Only when the water level of the underground water channel is higher than a certain level will it be opened, and the surplus water will be discharged to the Seine River. No wonder movies often have escapes from sewers. This place, not to mention crawling, is enough to perform a single acrobatics.