Musée des Égouts de Paris St-Germain & Les Invalides

Raw sewage flows beneath your feet as you walk through 480m of odoriferous tunnels in this working sewer museum, which underwent important renovations between 2018 and 2020. Exhibitions cover the development of Paris’ waste-water-disposal system, including its resident rats (there's 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.