The Museum: Paris developed its first sewage system around 1200 A.D., when King Philippe Auguste declared all streets be paved, with a drain running along the middle for waste. Today, some 1,300 well-organized miles of tunnels lie under the City of Light, and travelers can explore 1,500 feet of them on foot, via “sidewalks” running along the walls.
The Exhibits: Hold your breath and take the plunge—no, not literally!—to the city’s rather pungent underbelly (some say the stench isn’t as bad as you might imagine). While underground, be on the lookout for the wagon-vanne, a trolley that is essentially a manual flusher, helping to keep the canals clear of, ahem, debris.
Winter: 11a.m.–4 p.m.; Summer: 11 a.m.–5 p.m.; closed Thursday & Friday