I first learned of the Paris catacombs in a guidebook several years ago. The single paragraph describing the final resting place of some 6 million people was almost dismissive. But the photo of a wall -- made entirely of bones -- captured my imagination.

My macabre curiosity was finally satisfied one gray January day, when I found myself in Paris with a morning to kill.

Finding the entrance to the catacombs was an adventure in itself. It lies off the Place Denfert-Rochereau, a small concrete island in a tangled eight-way intersection. I walked its entire perimeter before I noticed a short line of tourists protruding onto the sidewalk. This was my only clue that on this quiet residential street lay the entrance to the underworld.

As I paid the 7 admission fee I saw a faded, typed sign warning people with respiratory conditions -- and bad hearts, and impressionable children -- to reconsider. Duly noted.

"Enjoy your visit," said the fellow who took my ticket. His friendliness caught me off guard. Parisians are not generally given to cheerfully greeting strangers -- especially (one would think) at the entrance to a mass grave. "Thank you," I said, smiling.

From what I'd read, I expected to tour a crypt like those found under most European churches. I also expected my visit to last 30 minutes or so. How long could it take to traverse a few bone-filled rooms?

The descent into a well

My expectations clashed with reality almost immediately as I started down the stairs. Broad stone steps turned into a narrow spiral staircase that plunged into the earth, like a well. The farther I descended, the moister the stone walls felt. All I could see below was an endless spiral of triangular steps, presenting themselves one after another.

The British couple ahead of me joked about getting dizzy. They had a point. As if on cue, the triangular steps opened onto a large landing. But my relief was short-lived; it was just a link to another spiral staircase.

I lost track of time, and my knees were starting to hurt. Later I'd learn that the stairs descend about 65 feet, or roughly six stories. But the constant spiral motion made it feel much farther.

The stairs finally stopped. In a series of brightly lit museum rooms, large posters traced the history of the catacombs, starting with the Romans. Over the centuries, these underground quarries -- les carrières de Paris -- have steadily expanded, like a giant spider web, beneath the city. Only a few sections contain bones, but most Parisians call the entire network "les catacombes" anyway.

Mercifully, only 2 miles of this sprawling network are open to the public. The rest of the tunnels, estimated to span 200 to 300 miles -- no one knows for sure -- are off-limits. That doesn't stop a few intrepid "cataphiles" from spelunking into manholes and shimmying under train tracks for a bit of subterranean adventure. Maybe next time.

The last poster mentioned that, among other notables, the Man in the Iron Mask is buried in the catacombs ... somewhere.

Entering the maze

The museum emptied into a dark tunnel. It was rectangular, with a low ceiling, and its limestone brick walls were illuminated by yellow incandescent bulbs. The air was thick and humid, the stone floor slippery with condensation. Everything had a slimy sheen.

I followed the British couple down the tunnel, but I was confused. Where were the bones? The tunnel began to snake. In some places the roof was arched; in others, the walls were chiseled directly out of the stone. Every so often the tunnel would veer abruptly. The only constants were the low ceiling, the moist air and the dim lights.

Occasionally I would pass a cavernous space that had been sealed off with an iron grate. A quick look beyond would reveal more passages, fading into the darkness. Others had been walled off entirely, the newer brick contrasting with the old. One grate partially concealed an artesian well that plunged another 20 feet into the ground.

In stopping for a closer look, I'd lost the Brits. I was alone. But I wasn't too worried. On this one-way tour, the detours had been sealed off. There was little chance of getting lost; all I had to do was keep walking. Still, I wondered ... where were the bones?

The tunnels were silent, except for my footsteps on the moist, crunchy gravel. In the gloom, I noticed a new feature: A thick black stripe had materialized on the ceiling. It appeared to be soot, perhaps left over from a parade of passing torches.

I heard voices. The Brits were standing in a well-lit gallery. Into its stone walls, a quarryman named M. Décure had long ago carved two elaborate sculptures. One depicted the fortress of Port-Mahon, where he had been held prisoner by the English army. His sculptures were labeled and protected by a small fence, like paintings in a museum.

Then came the real deal.

Into a massive tomb

Just around the bend was a cavernous room with several square pillars, each painted black and white. Beyond the pillars lay a portal with the same bizarre paint job. The sign above the door read, in French, "Stop! This is the empire of the dead."

This sounded promising.

I entered the empire of the dead only to be greeted by a guide. But I barely noticed him, or the other tourists milling about. I was finally seeing with my own eyes the image that had so captured my imagination years ago.

Bones -- thousands of human bones -- were carefully arranged and stacked into the walls. The incandescent lights gave them a deep amber cast.

I stood for a few moments, transfixed by the dead, before I again became aware of the living. With stiff arms, the Brits were pointing their camera at themselves, struggling to take a self-portrait. I offered to snap a picture or two, and they gladly repaid the favor. Only later did it strike me as odd that we were smiling, mugging for the camera, in a dark, damp mass grave.

Glee among the gloom

The guide rejoined us. In richly accented English, he offered to shine his flashlight on some of the more interesting bone patterns. Like the guy who had taken my ticket, the guide was disarmingly upbeat. "See? Look here," he said, motioning with his flashlight.

"The bones are made to look like a face. Be tall so you can see better." Sure enough, someone's femurs had been combined with someone else's cranium to look roughly like Mr. Burns from "The Simpsons."

"Come, look here," he said, beckoning with his flashlight. "Here we have a heart -- un coeur, ça fait un coeur."

His enthusiasm was infectious. The Brits and I snapped photos and expressed our appreciation.

"This is your job?" I asked him as the British couple moved on. "You do this every day?" He smiled and nodded energetically. "Yes. Six million co-workers, but none of them ever talks to me." I laughed and thanked him, but he was already greeting the next pair of visitors.

Necessity: The mother of interment

My trek through the tunnels had been good practice for what lay ahead. There were still lots of tunnels -- but now the walls were made of bones instead of bricks.

At first glance, the neatly stacked bones appeared to be recessed slightly into the walls, stretching from the floor almost to the ceiling, to a height of about 5 feet. But then I noticed some piles that didn't quite reach the same height.

Peering into the gap between the bones and the ceiling, I saw a room about 20 feet wide and just as deep. The meticulous care with which the bones in front had been arranged belied the jumbled chaos in the back. Bits of ribs, vertebrae and other assorted small bones jutted randomly out of a giant, tangled heap.

This explained why the intricate façades, with their ornate macabre designs, contained only leg bones and skulls.

Occasionally, the tunnels would open unexpectedly into larger galleries with imposing names, like the Crypt of the Sepulchral Lamp. Other galleries contained memorials resembling tombstones. One honored the memory of Philibert Aspert, who got lost in the catacombs in 1793. His body was found 11 years later, just a few yards from an exit that was concealed in the darkness.

By some estimates, the Paris catacombs contain the skeletons of 6 million people. Most of the bones came from cemeteries around Paris, which by the mid-1600s had become so overcrowded that they were causing outbreaks of disease. The worst was Les Innocents, which occupied the area now known as Les Halles. After accepting more than 4 million bodies over 30 generations, Les Innocents had finally exceeded its capacity. Some accounts even describe bones and bodies popping out of the ground.

In 1785, Police Lieutenant General Alexandre Lenoir hatched a plan to condemn the cemeteries and move the remains into the abandoned stone quarries that lay beneath Paris. Beginning in April of 1786, the cemeteries' contents were transferred discreetly -- under the cover of night, and always accompanied by a convoy of priests. By the project's completion in 1814, millions of bones had been quietly relocated underground.

Alone among the masses

Now considered a museum, Paris' catacombs draw a steady stream of visitors from around the world. On this particular January day, visitors were few. Apart from my British friends, the only other tourists I saw underground were a couple from Spain, a group of French kids and a trio of Japanese women dressed for corporate success.

But I was grateful for the solitude, for the chance to move through this strange place in silence and at my own pace. It gave me time to read the plaques that noted the origin of each pile of bones.

Looking at the dates, I reflected on how these people had met their ends. How many were cholera victims, from the 1848 epidemic? How many of these women had died in childbirth? And how many of these young men had succumbed to the plague, or to consumption, as tuberculosis was once called?

I paused at a stack labeled "Combat ... Faubourg St. Antoine ... 1789." These bones told a different story. A few skulls showed evidence of bullet holes -- sometimes more than one. Others had been smashed. Two hundred years later, they still bore testament to the horror that is war.

How strange -- and how fitting -- that peasants and writers, monks and architects, children and revolutionaries, should all end up mingled like this. It was a sobering reminder that, no matter our age or education or wealth or achievements, the same fate eventually awaits us all.

Back to life, already in progress

The tour was almost over. I exited the ossuaries and found myself standing in awe at the base of a huge bell-shaped chamber, looking up at several stories of successive brick arches. Only later did I learn this had been the site of several cave-ins, and that the brick arches were buttresses that reached almost to street level. Just as well they should omit that from the brochure.

The climb out of the catacombs took considerably less time than the descent. Apparently those snaking tunnels had been working their way back up toward the surface all along.

Dazed, I emerged from another unremarkable doorway onto a residential street a mile from where I'd started. I squinted as I walked down the sidewalk in the midafternoon light, looking for the familiar "M" that would mark the entrance to a Métro station, and the beginning of my journey home.

As I stood in the Métro tunnel, waiting for my train, I thought of the millions who lay just on the other side of that white tiled wall. In Paris, so thin is the boundary between the daily commute and eternal rest.

Editor's note: Vandals broke into the catacombs in early September, scattering bones in an "incomprehensible and revolting" attack, according to the director of the site, Jean-Marc Léri. The catacombs are now closed to the public indefinitely.