Les Égouts de Paris
This popular underground museum brings you into a portion of the city's 1,300-some-mile sewage system, along murky, slightly odorous waterways carrying you-don't-want-to-know-what on its way to disposal. Giant iron balls and antique flushing machines are on show (both used to clean the system), while panels detail sewer history from the first underground system of 1370—originally aimed at keeping cholera, the plague, and other less deadly but still debilitating diseases at bay. Most of the praise goes to Baron Georges-Eugène Haussmann, who modernized the city between 1852 and 1870 and whose égouts—the French word for sewers—are considered among his finest work. Indeed, he figured out how to bring in potable water and drain away wastewater by creating a system beneath the city that resembled a city. If nothing else, you'll appreciate how far we've come from the Middle Ages, when sewage disposal involved tossing a chamber pot's contents out the window and shouting "Gardez l'eau!" to warn those on the streets below.
Pont de l'Alma, face 93 quai d'Orsay, 01-53-68-27-81, closed Thurs.-Fri., www.paris.fr, 4.30 euros. Metro: Alma-Marceau
Les Catacombes de Paris
Deep beneath the bustling cafés of Montparnasse's Place Denfert-Rochereau lurks the eerie world of the catacombs. Once part of old limestone quarries, the catacombs are a small portion of a 180-plus-mile maze of tunnels; they served as a depository for the disinterred bones of some six million Parisians that overcrowded city cemeteries between 1785 and 1860. This ossuary is not for the skittish. Walking along the low-ceilinged, dimly lit passageways dripping with water, tourists pass bones that are artfully stacked ten feet deep by kind (tibias here, femurs there) and punctuated with vacuous skulls. Markers indicate the origin of each bone stack—those from the old cemetery of the Madeleine may (or may not) include the remains of Marie-Antoinette and Robespierre.
Napoleon I built the Canal St.-Martin in the early 1800s to shortcut the meanders of the Seine, as well as to provide fresh water to a growing population. Haussmann later brought a portion of the originally open-air canal underground. Visitors can explore the three-mile-long canal by hopping aboard a glass-sided boat at Port de l'Arsenal, Paris's yacht harbor, and delving into the watery darkness of a 19th-century tunnel beneath Place de la Bastille. Directly overhead, a crypt contains the remains of 500-plus victims of the 1830 revolution (their names are inscribed on the Colonne de Juillet, aboveground). After about a mile, the canal hits open air, where the rest of the three-hour cruise moseys through a peaceful realm of graceful wrought-iron bridges and eight locks, past such historic landmarks as the Hôtel du Nord and the Hôpital St.-Louis.
Bassin de la Villette, 13 quai de la Loire, 01-42-39-15-00, www.canauxrama.com, check website for departures, 16 euros. Métro: Bastille (tour also leaves from Bassin de la Villette, Métro: Jaurès)
Crypte Archéologique du Parvis de Notre-Dame
In the 1960s, ruins beneath the plaza fronting the cathedral were excavated. They are now displayed in situ in the underground crypt museum. Among them: the foundations of Paris's oldest rampart (third century A.D.); Roman house fortifications, including a small tiled floor (second and third centuries); and the basement of the old Hôtel Dieu (14th century). Scale models and descriptive panels provide an excellent progression of Paris through the ages.
Musée National du Moyen Age
The Romans who lived in Lutèce (present-day Paris) are remembered by their thermal baths, the largest ones of which were in use between the first and fourth centuries A.D. and partially incorporated into the 15th-century Hôtel de Cluny, today the National Museum of the Middle Ages. The best-preserved room—the high-vaulted frigidarium (cold room), with hints of original frescoes and mosaics—as well as other Gallo-Roman rooms now hold precious medieval art. See more of the baths' underground ruins on a guided tour, offered 2 p.m. on Wednesdays.
6 place Paul-Painlevé, 01-53-73-78-16, closed Tues., www.musee-moyenage.fr, 8 euros. Métro: Cluny-La Sorbonne, Saint-Michel, or Odéon
Beneath some of the world's greatest masterpieces, in the basement of the Louvre, you'll find the excavated foundations of the royal castle that stood on the site from 1190 to the beginning of the 16th century. In the dimly lit space, you can stroll around the perimeter of the medieval moat, past the beautifully restored stone ramparts, and into the dungeon. Don't miss the cavelike Salle St.-Louis, all that remains of the medieval interior, with its elegant columns and vaulting.
34-36 quai du Louvre, 01-40-20-53-17, closed Tues., www.louvre.fr, 9.50 euros. Métro: Palais-Royal–Musée du Louvre
More than 130 miles of train track zigzag through 300 stations and interlocking tunnels beneath Paris, a system first initiated in 1900. A métro ticket takes anyone through this vast subterranean labyrinth, filled with frenetic subway patrons, musicians playing for euros, and graffiti galore. A walking tour offered by ADEMAS (Association d'Exploitation du Matérial Sprague) provides insight into the subway's history and art nouveau design, and—the best part—a visit to one of the "ghost" stations unused since World War II, where advertisements promote long-discontinued products. Check the website for the next tour, offered on occasional weekends.
Association ADEMAS, 15 rue Erlanger, e-mail: email@example.com, 12 euros