Raiders of the Lost Toilet Factory

"That's weird," I say, venturing a closer look. "I wonder why they do that."

The cockroach conclave is the first of many times I wonder aloud at some discovery. Alex had prepped me as best he could for what to expect, but the network we're exploring to the west of downtown Dallas turns out to harbor an endless supply of mysteries.

"That's how it is down here," Alex says. "Everything I think ends with a question mark."

Equipped with rubber boots and flashlights, we'd followed a sunken stream bed running alongside a commercial building to get to the two arched, gaping tunnel mouths, each delivering a flow of water less than an inch deep. Our first choice eventually narrows into a bell-shaped channel less than 4 feet high, and we decide to turn around to explore the other one.

The second tunnel, however, isn't exuding the benign wet-concrete smell of the first. Instead it has the nauseating stench of a brown-water sewer. I hesitate to enter, but Alex is undaunted. As it turns out, the source of the fetid water is a side tube just 20 feet into the tunnel, and as we continue upstream the smell recedes. Still, I wonder if sewer gas collecting in the tunnel might pose a threat.

"The thing about drains is that they're all sloped," Alex assures me. "All those gases just go straight up and out the manhole covers and drain grates."

Later I find out that isn't always the case. In an interview, Dallas storm drain inspector Roy Bruce recalls an incident years ago when some kids exploring a drain ignited trapped gases with a lighter and suffered horrible burns. Afterward, Bruce was assigned to see if the flash had damaged the tunnel.

"That was real creepy," he says. "You could see the bloody handprints where they were stumbling against the walls when they were trying to get out."

Blissfully unaware of this precedent, Alex and I continue to march up the tunnel. At its mouth the tube is easily 15 feet in diameter, but after a small room marking a turn in its course, it narrows to perhaps 10 feet wide.

Alex begins peering up the various side passages, looking for light shining in through a roadside drain. He wants to take a GPS reading, an invaluable tool for calculating the distance and route we've traveled. When he spots daylight, we head to the source, forced to move in a backbreaking crouch through the narrow passage. The light shines down from a room overhead, and Alex hoists himself up to take a reading. He's always careful not to be seen, eager to avoid well-intentioned calls to 911 reporting someone stuck in the drains. Quickly he turns to me below, putting a finger to his lips.

"There's a guy," he breathes, almost mouthing the words, "walking his dog." He snaps a digital picture and passes the camera down to me. On the small screen there's the guy, facing away from the drain, unaware that eyes are studying him from below ground. Something about the situation fills us both with silent laughter.

A few hundred yards farther on, still in comfortable 10-foot pipe, we come to what can only be described as The Lid. The mouth of our tunnel opens into a large brick-walled room. Three more large openings beckon, but the room is dominated by a massive concrete disc, 10 feet in diameter and 6 inches thick, lying on the floor like a gargantuan quarter. Its edges are lined with black tar that corresponds to a ring around the tunnel mouth we had just left.

For some reason, the city of Dallas had seen fit to cap off this enormous trunk line of the storm sewer with a giant concrete lid--and then open it up again.

Why? We couldn't have been more perplexed if the room were wallpapered with $100 bills.

Later I ask Roy Bruce if any large storm drains had removable lids or would be temporarily closed for any reason anywhere in Dallas' estimated 2,500 miles of storm drains.

"Naw," he says. "There's nothing like that down there."

We push upstream, and after a half-hour the pipe is still a roomy 8 feet wide. We pass a side pipe delivering a trickle of water. The floor beyond is completely dry.

"That's a good sign that it's probably blocked off up ahead," Alex says. Sure enough, a dozen yards farther we encounter a claustrophobe's nightmare: The tunnel is permanently sealed by a wall of bricks set in concrete. We have access to a side tube that seems to bypass the barrier, but it is dauntingly narrow, so we decide to turn back.

The weather is always two days behind in the storm sewers. At least that's what Alex tells me, and I can't deny that the temperature underground more closely matches the sunny spring weather of two days ago than the cloudy, chilly atmosphere that now prevails topside. This is one of two laws Alex has formulated in his years of exploring the tunnels.

The other is that the farther upstream you go, the smaller the pipes get--which is why I'm scratching my head again back in the Lid Room. We're facing downstream, yet one of the tunnels in front of us is smaller than the upstream one we've just come out of.