Raw sewage flows beneath your feet as you walk through 480m of odoriferous tunnels in this working sewer museum. Exhibitions cover the development of Paris’ waste-water disposal system, including its resident rates (an estimated one sewer rat for every Parisian above ground). Enter via a rectangular maintenance hole topped with a kiosk across the street from 93 quai d’Orsay, 7e.

The sewers keep regular hours except – God forbid – when rain threatens to flood the tunnels. Toy rats are sold at its gift shop.