The catacombs of ancient Rome served as houses of worship for Jews and Christians. In the early 1800s, the sewers of Paris yielded gold, jewels and relics of the revolution. Closer to home, thousands of people lived in the subway and train tunnels of New York City in the 1980s and ‘90s.

Beneath the neon, what secrets do the Las Vegas storm drains keep? Armed with a flashlight, tape recorder and expandable baton for protection, I sought to answer those questions. It all started in the summer of 2002, when I explored five storm drains, and it culminated in the summer of 2004, when I explored the flood-control system in full. It continued through 2006, as I returned to the drains for follow-up notes and to investigate virgin tunnels.

When I came up with the idea of exploring the storm drains, after reading about a fugitive who used a drain to elude the police, I didn’t consider that they might be inhabited. I couldn’t make that connection; it was too remote for a boy from the middle-class South. I expected to find concrete, darkness and water, and lots of miscellaneous items, like maybe a wallet and wig, or graffiti and stray animals. I didn’t expect to find people. People sleep in houses and hotels, motels and -- a local favorite -- trailers. The more desperate among us sleep in shelters, public parks and under bridges.

But they don’t hang out in dark concrete boxes that run for miles and miles or sleep in concrete boxes that fill with floodwater. Except that hundreds of them do.

Exploring the drains with writer Josh Ellis, we interviewed some of their inhabitants, including junkies, hustlers, people down on their luck and Vietnam vets, and after a while, it almost began to make sense. The drains are free, ready-made reliable shanties –- a floor, two walls and a ceiling. They provide shelter from the intense Mojave heat and wind -- don’t forget, most desert animals live underground. Some of the drains remain dry for weeks, even months, and cops, security guards and business owners don’t seem to want to roust anyone beyond the shade line.

But ultimately, the drains can be deathtraps. They’re disorienting and sometimes dangerously long. Many of them run under streets and contain pockets of carbon monoxide. They can be difficult to exit, particularly in a hurry. They’re not patrolled. Who would work that beat for any amount of money? They’re not monitored. There are no rules. There are no heroes. And, oh yeah, they can fill with floodwater at the rate of one foot a minute.

Walking into a storm drain is like walking into a casino: You never know what’s going to happen, but chances are it isn’t going to be good.

But the flood-control system, an intricate web that spans from mountain range to mountain range, wasn’t all bad. I learned a lot about Las Vegas, Las Vegans and myself down there in the dark. There are about 300 miles of drains in the Las Vegas Valley, some of which are more than five miles long. While walking on mile-long straight-aways that felt like concrete treadmills, I thought about the ephemeral nature of Las Vegas. There are the old bungalows being bulldozed for high-rises; friends who appear and then disappear, the Dunes, Sands and Desert Inn demolished recently in clouds of dust. This city eats its children, I thought. Everything here is as disposable as a razor blade, except for the storm drains. They’re our preservation areas. Our art galleries illuminated by daylight falling through grills overhead, our time capsules. For me, they were also a classroom.

I followed the footsteps of a psycho killer. I two-stepped under the MGM Grand at 3 in the morning. I chased the ghosts of Las Vegas legends Benny Binion, Bugsy Siegel, Elvis, Frank Sinatra and Howard Hughes.

I discovered that a manhole can feel a lot like heaven. That in some ways, I prefer underground Las Vegas to aboveground Vegas. It’s cooler, quieter and there’s a lot less traffic. That maybe the afterlife is just a matter of trading in your body for a new-and-improved model. I learned how people make methamphetamine. That art is most beautiful where it’s least expected. And that there are no pots of gold under the neon rainbow.

Matthew O’Brien is news editor of Las Vegas CityLife, and author of the new book, Beneath the Neon: Life and Death in the Tunnels of Las Vegas.