When the sewers of Paris get clogged with putrid waste, they're sometimes cleaned the same way they were over a century ago: with a giant, rolling ball.

Models of these iron and wood "boules de curage" are on display at the Paris Sewer Museum (Musée des Égouts de Paris), which is a working sewer station that lets visitors explore the evolution of this hidden infrastructure. The museum is accessed through a rather unassuming stairwell at the Quai d'Orsay, something which almost vanishes into the waterfront not far from the Eiffel Tower and the Jean Nouvel-designed Musée du Quai Branly with its pristine gardens by the Seine.