Surliness in cafés and restaurants was the only part of our Paris vacation that went according to plan last summer. The weather was unseasonably foul, causing chronic delays and postponements at the French Open—to which we could not get tickets. The Métro, the city's subway system, was sporadically shut down by striking workers. Another labor stoppage forced the closure of the city's museums, which was rather more upsetting to my wife, Laura, than it was to me, though I put up a good front. You mean we're just going to have to spend more time sitting in cafés, people-watching, and forgetting the names of our children? Darn the luck.

Our cultural options were narrowed, we found, but hardly closed off. We discovered that in Paris, perhaps the world's best walking city, you can't really go wrong. We took a walking tour of the Marais district, where we saw the city mansion of a certain Madame de Granvillier, who in the late 17th century poisoned her father and two brothers and was subsequently executed on the Place de Grève. We scoured the Montmartre, where we were transported by the songs of a chorus of nuns at Sacre Coeur, if not up the hill to the cathedral by escalator, which was out of order. And then, like Jean Valjean, the escaped convict and protagonist of Victor Hugo's fat classic, Les Misérables, we went underground.

Strolling west along the Left Bank of the Seine one gloomy day, as we approached the Pont, or bridge, d'Alma, we noticed a sign that said Les Ègouts de Paris. There, in the shadow of the Eiffel Tower, was a booth where, for a mere $3, one could purchase a ticket to the Paris Sewer Museum. Leave it to the French, long regarded by the rest of the world as a nation under the impression that its waste doesn't stink, to elevate a sewer system to tourist attraction. (The catacombs of Paris, another stop on our underground tour, proved equally riveting, if less nose-wrinkling.)

Our decision to visit les égouts seemed counterintuitive, a bit perverse. Who comes to the City of Light to go underground? We did, and so should you. Anyone who has taken the elevator to the top of the Eiffel Tower, or taken in Quasimodo's bell tower view from atop Notre-Dame, might enjoy seeing this European capital from a different vantage. Every Parisian street lies atop its own corresponding sewer, complete with its own underground street sign. It is a city within a city, a dank, fascinating demimonde from which one emerges blinking and thinking, "Now that was cool."

The Paris Sewer Museum takes you through 500 yards of the city's 1,300-plus miles of sewers. For all but the most passionate waste management aficionado, that is enough. Visitors can admire the tools of the sewer man's trade—the flusher trolley, the two-ball traveling cleaner, the gas mask. They are also provided with a brief history of Paris's methods of waste disposal dating from the present—the system evacuates 1.2 million cubic meters of wastewater per day—back to the Middle Ages, when those methods consisted of shouting "Gardez lou!" before hurling the contents of one's chamber pot out the window.

Be grateful, as you take the 41 steps down into the sewers, that you are not carrying a wounded rebel over your shoulder, as was Valjean when he entered this underworld. The odor, while tangy, is not overwhelming. If you take the Paris Walking Tour of the sewers, as we subsequently did, don't be alarmed when guide Peter Caine opens his remarks with the question: "Everyone got their nose plugs?" He is just kidding.

The ensemble sported by the Paris sewer workers, les égoutiers consists of cheery, yellow hip waders over blue jacket and matching hard hat, to which a headlamp is affixed. You might think that theirs is a stinking job. Wrong. Les égoutiers put in 30 hours a week and they are rewarded by the government with very generous benefits, such as no-interest loans for the purchase of a home. They are well regarded and appreciated by the citizenry—especially since their three-month strike in 1977.

A resolute-looking égoutier mannequin at the entrance of the Galerie Bruneseau pilots a wagon-vanne, or flusher trolley, a 20-foot apparatus equipped with a manually operated valve which generates a flushing action, the better to move the sewage along. (Pockets of trapped gas make combustible engines in the sewer a bad idea.) As you follow the sidewalk through the Galerie Bruneseau, you may or may not wish to cast your gaze upon the turbid water flowing alongside.

The man for whom the gallery is named was a giant in sewage annals and a real-life friend of Valjean's creator, Victor Hugo. During the reign of Napoleon, Pierre Bruneseau, the city's municipal works inspector, spent seven years mapping and charting the sewer system, also known by its Latin name, the cloaca. This 1,300-mile network, dating back some 400 years, had been constructed piecemeal. No map of it existed. Even the police of Bruneseau's day refused to enter these caves, which were as foreign and mystifying as a bidet in Bozeman. They were, according to Hugo, "tortuous, fissured, unpaved—interrupted by quagmires, rising and falling illogically, fetid, savage, wild . . . nothing equaled the horror of this old voiding crypt." Within it Bruneseau discovered, among other things, ancient dungeons and the skeleton of an orangutan that had escaped from the zoo in 1800. It is little wonder that upon completion of the project in 1812, Bruneseau was lauded as "The Christopher Columbus of the cloaca."

While vivid, Hugo's passage on the history of the Parisian sewers is not as comprehensive as what can be found in the Galerie Belgrand. It features a "history of the water cycle" display that is flush, as it were, with tidbits on sewer-related contributions made by various emperors and monarchs throughout the city's history. We learn that Hugues Aubriot, merchant provost, directed the construction of the city's first vaulted sewer in the late 14th century. His newfangled sewer, unfortunately, decanted its waste into the Seine just below the Louvre, offending Louis XII and later forcing François I to move his mother to the Tuileries, to escape the aroma. By the mid-16th century, says Kelly Spearman, an art historian who lives in Paris, the stench emanating from one stretch of the Seine, the Right Bank of the river between the Pont Neuf and Pont au Change, became known as "le quai de la mégisserie"—the riverbank of the appalling stink. "You had people fainting in the street, it was so bad," Spearman says. The once-fashionable Marais, downwind, was deserted by the wealthy, who could no longer bear la mégisserie.

Periodic expansions of the sewers failed to contain the problem. The infamous backup of 1802 reached a statue of Louis XIV before stopping just short of the house of Racine, enabling wiseacres to remark that the sewers respected the poet more than the king. By this time the population of Paris was 700,000. All of the city's sewage was dumped into the Seine, from which Parisians drew most of their drinking water. These two factors had much to do with the cholera epidemic of 1832, which killed 30,000 people.

To the rescue came the man for whom the Galerie Belgrand is named. Eugène Belgrand was placed in charge of the city's water department in 1854 by Baron Georges-Eugène Haussmann, the legendary prefect of the Seine. Belgrand is responsible for the system's signature characteristic: He designed a network of gravity sewers which make maximum use of the land's natural slope. At key points throughout the system, catch basins trap solid waste, which is then moved out of the city by truck. He also designed the cleaning machines used by the sewer men to this day. In a large photograph in the Galerie Belgrand, five modern-day égoutiers are pictured emerging from a manhole, smiling, their shift over.

After picking up a few postcards from the souvenir shop, or "sewer-venir store," as our pun-happy guide put it, we took leave of les égouts. Few breaths are likely to be sweeter than those first drawn upon emerging from the sewers. If you wish to trace the steps Laura and I took after our tour, take a 20-minute stroll down the Boulevard Saint-Germain. Have a seat at Aux Deux Magots and watch the street life. If the Parisians around you seem just a little more cosmopolitan, more chic than you, it can be comforting to remember that to les égoutiers, we are all equals.

The equality point is made some 6 million times in another offbeat underground exhibit we took in the following day. After taking the Métro to the Denfert-Rochereau station in Montparnasse, we crossed the Boulevard Raspail and found the entrance to the catacombs of Paris.

The entrance fee, $4.50, seemed a small price to pay to gaze upon the bones of Robespierre and Marie Antoinette. The fact that their remains are only probably down there, mingling with all the other bones of the 5 to 6 million Parisians reposing in this cavernous, common tomb, makes it no less eerie or surreal.

Once again, we happily followed an English-speaking guide from Paris Walking Tours, who informed us that this dig, at what was once the city's southern border, had been a quarry for gypsum and limestone until the late 18th century. But there was a problem uptown. Les Halles, the city's main food market, was adjacent to its largest common cemetery. So crowded had the soil become with the deceased that it was losing its ability to break them down. "People were asphyxiating in their cellars from gases," reported our chipper guide, making the cavern walls seem just a bit narrower.

In 1785 the shy, ineffectual Louis XVI, an avid hunter and locksmith, ceased the pursuit of his hobbies long enough to order that the dead henceforth be disposed of in this quarry, which would later become the probable final resting place for him and his wife, Marie Antoinette. When other cemeteries suffered overcrowding problems, or got in the way of Haussmann's new boulevards, the deceased were disinterred and redeposited in the catacombs, which served as the city's central bone depository until 1860.

After descending 83 steps below the street, you spend 10 minutes following your guide through a dimly lit maze. Keen-eyed visitors will notice a black line on the ceiling—residue from candles: The catacombs were opened to tourists in 1804. In those days, more than 200 miles were open to the public. "People got lost," said our guide, who told us, with the practiced timing of a camp counselor, of the porter who disappeared into the tunnels. "They found his skeleton 11 years later. He was identifiable only by his keys which were lying nearby." I have been lagging behind, scribbling notes. I make a mental note to not stray from the group.

By then we'd been underground a quarter of an hour and seen not a single bone. Then we arrived at an arch, above which a warning is etched in stone: Arête! C'est ici l'Empire de la Mort—Stop! This is The Kingdom of the Dead. Stacked and packed, neatly arranged—fibulae here, tibiae there, crania over here—are literally millions of bones. Regularly interspersed monuments tell you where the bones around it are from. Here are the bones, or ossements, of prisoners massacred during Robespierre's Reign of Terror, there are the bones of workers killed in a 1789 labor uprising.

The tablet which says "Ossements de l'ancien cimetière de la Magdeleine" merits special scrutiny. It was in this mass grave, near what is now the Place de la Concorde, that the bodies of, among others, Robespierre, Marie Antoinette, and her husband were thrown. Twenty-two years later, workers were sent into that cemetery to retrieve the famous corpses.

Whoever dug up the bodies almost certainly came out with the wrong ones. Which means the bones of the woman who supposedly said, "Let them eat cake," are in these stacks. How often do you get to contemplate the remains of royals?

Other benefits from our subterranean snooping: We learned as much about the city's history, if not more, than we could have in some well-ventilated, brightly lit museum. Our skin, as Laura pointed out, was not prematurely aged by overexposure to the sun. And when we got home, we could tell our 3- and 5-year-old, whose names we eventually recalled, that we saw real skeletons, and the place under the ground where everything goes after you flush the potty. They're still asking us about it.

We felt sufficiently enriched by our underground excursions that it only hurt a little when, on the morning of our departure, our beloved concierge, Gilles, saw us in the lobby and said, "Good news! The museums are opening today!"

If You're Going . . . Entrance to the Paris Sewer Museum is at Pont d'Alma in front of 93 Quai d'Orsay, near the Place de la Résistance. Or visit www.pariswalkingtours.com. The museum is open Saturday through Wednesday from 11 a.m. to 5 p.m. (it closes at 4 p.m. from October through April, and shuts down for three weeks in January.) For information on travel in Paris or elsewhere France, contact the French Government Tourist Office (310) 271-6665.