"It would be nice not to end up in jail," Siveya says calmly as we scan online city maps, trying to decide where our first venture into the San Francisco underground might be. "Or worse."

"Yes," I agree, trying to sound equally chill. "That would be good."

It's this exchange, over my second cup of tea at Siveya Ethersmith's Victorian apartment, that makes me realize this urban exploration stuff is no joke.

I've been hearing about these urban explorers for years, but Siveya is the first real one I've met. He has been obsessively surveying the abandoned insides of urbanscapes, from old subway tunnels to shutdown hospitals, for about two decades. He took a brief hiatus to write a memoir, The Giving Thief, about his adventures. But now that the memoir is near done, he has agreed to take me with him on his first underground mission in months. I haven't been so excited about anything since the first time I teepeed my neighbor's yard in junior high.

Urban Explorers have been around as long as there have been cities, but many see the 1970's San Francisco-based "Suicide Club" as the progenitors of modern urban exploration. The Suicide Club's motto was to live everyday as if it was their last, which spurred acts like climbing the Golden Gate Bridge to have a picnic, riding trolley cars naked, and spending significant amounts of time at a secret underground military base that is allegedly hidden beneath San Francisco, abandoned for decades.

Members of the Suicide Club claim to be the only ones who know where the base, probably built around World War II, is located. The club took the History Channel inside the base, a clip that's on YouTube, but blindfolded the film crew until they were underground so they didn't reveal the location.

"I can't believe these Suicide people get to enjoy the base all to themselves," Siveya says with an envious grin. He's determined to find the entrance, but this being my first adventure, we'll start a bit more humbly. Chinatown is allegedly riddled with tubes and passages that the locals may even still use, but we're not feeling up for confronting any illegal smuggling and potentially having a language barrier to explain ourselves.

The Prohibition Era produced some secret passageways and there is rumor of a long secret tunnel that used to run under California Street and come up at the elite men's club Pacific Union Club. The trick is finding one of these things. Siveya has found online clues to the location of an abandoned train tunnel that was built in the early 1900's and shut down around the 70's. It seems like a good entry-level adventure so we've agreed to start there.

The fun of urban exploration is finding secret spots, so I'm going to keep the exact location of anything we find intentionally vague. Our only clue at this point is an online photo of one of the tunnel entrances and a description of the northern neighborhood the tunnel runs through. Siveya thinks he recognizes the entrance as being close to a popular supermarket. The photos show the entrance shut down with tall metal gates, a possible space to squeeze through between the tunnel arch and the top of the gate, but it's hard to tell. "I'm good at lock-picking too," Siveya offers.

We pick a Wednesday night around 10 PM to check it out. Nathaniel Eaton, another local writer who likes mischief, joins us. It's dry when we get in our cars, but it has been raining on and off all day. The streets are wet, dark, and empty.

We park at the supermarket and walk quietly through a nearby park, the yellow glow of streetlights casting long shadows. I have the exact same feeling I used to get sneaking out to roam the streets as a teenager. It's a feeling I've missed.

The tunnel entrance is easy to find. It's huge and out in the open, a mouth that must be 23-feet high and almost just as wide. Unfortunately, it's surrounded by a chain link fence and gated with 12-foot-high metal doors. The space between the top of the metal door and the arch is barricaded with more fencing. There's also a security guard for a nearby parking lot about 15 yards from the entrance who could easily spot us.

We decide to look for the other entrance, which we know from the description of the tunnel is about 1500 feet to the east. Walking through the park, we come to a vista that overlooks the waterfront. It begins to rain and storefront lights sparkle on the bay. It's magical and silent. Nathaniel is recounting an urban exploration legend from New York he read about. Apparently, a ballroom-sized room was found beneath Manhattan with a perfectly-tuned grand piano.

We're not even in the tunnel yet and I think I'm sensing what Suicide Club leader Gary Warne meant by describing urban exploration as a "super reality," akin to making a film or fantasy come alive.

We descend a muddy hill to the waterfront. The street is oily and shiny, drops of rain spackling the puddles. Adrenaline has my senses working double-time. I feel like I'm in a graphic novel.

The other entrance to the tunnel is right where we'd guessed, but this side has no fencing around it, just the 12-foot metal doors and a gaping hole above that would be easy to fit through.

There's a police car nearby with sirens on, busting someone. The cop drives slowly by. Siveya starts pointing to a sculpture as if we're sightseeing. Nate and I pull out our iPhones. The cop doesn't stop. "That's the nice thing about doing this stuff when you're older," says Siveya. "We don't fit the profile of who the cops are looking for anymore."

The cops move out of sight and we wander back to the tunnel entrance. The coast seems clear. Using the big metal door hinges, I get a foothold and lunge for another hinge, pulling myself up onto the top. I shine my flashlight into the tunnel. It's huge and black and smells of old mud. I'm straddling the top of the door when Nate whispers, "Somebody's coming, hold on!" I can either jump down from my perch or climb inside the tunnel. Screw it, I've come this far.

I clamber down into the darkness, groping for handholds, and land solidly on the tunnel's dirt floor. A rush of excitement. I'm in. But it also hits me that I'm in alone. My mind wanders back to Siveya's stories of freaky homeless people lurking in places like this. "That's the most dangerous part," he'd said. Damn. I whistle to see if I hear anyone rustle or call back in response. Nothing.

Siveya climbs up the gate and descends to the other side more gracefully than I did. Nate watches him, and seeing that it took all of his 6-foot plus height reaching to make it over, decides he's just going to just keep watch, probably a good idea.

Inside, Siveya flips on his head-lamp and reveals a big grin. "Here we go," he says. And just like that, we are officially walking a secret underground tunnel in San Francisco. Weird. We can see the other end 1500 feet away. It reminds me of death, "the light at the end of the tunnel."

We walk slowly forward, investigating every etching of graffiti, every empty bottle, every muddy shoe. We are detectives, anthropologists searching for civilization. Why this tunnel isn't open to the public is the first question that hits me. How many other secret passages go unused in this city?

We walk the whole tunnel in about 15 minutes and don't find anything remarkable, just a family of raccoons that seem more scared of us than we are of them. They scrape at the tunnel gate, unable to climb out from this angle. We decide to stop scaring them and go back.

I feel a sense of accomplishment, but after that fantastic shot of adrenaline, I'm already flipping through the moments leading up to entering the tunnel, trying to hang on to that feeling. Siveya, perhaps on the same page, is talking about trying to find that secret underground military base. We theorize about where it could be: Golden Gate Park, The Presidio, The Headlands? I start feeling that rush of the unknown returning.

"You game for starting to look?" Siveya asks.

"Definitely," I say, happy we've only scratched the surface of the underground.

Tours of the underbelly are offered in many major cities, from Portland's infamous Shanghai Tunnels to Seattle's spooky underground city to Manhattan's forgotten subway stations. Petition your Supervisor to get some of San Francisco's underground spaces opened up for public tours.

Design:  Majorminor

Tunnel photo by  Steve Jurveston