Paris Sewer Museum

In Paris, there is a sewer museum. It's called Le Musee des Egouts de Paris.

Located in the sewers below the Quai d'Orsay on the Left Bank, the museum takes you to see Paris's public works system which date from 1370. Don't worry, the sewers have been upgraded since, and include the refurbishing of the sewers in bad condition, the renovation of the pumping stations, and construction of new sewers. It has now 2,100 kilometers of tunnels and supplies drinking and non drinking water mains as well as telecommunication cables and even traffic light management cables.

[Sources: Wikipedia, Europe for Visitors]