I'm in the lost-and-forgotten Knox Street station waiting for the DART train.

Before I can follow the DART tunnel crew down the tracks, they want the northbound train to Mockingbird Station to pass.

Some 80 feet below busy North Central Expressway, it's dark, and hot and dirty in the hole that was dug to be Dallas Area Rapid Transit's commuter rail station for the Knox-Henderson neighborhood.

A red light signals the approach of a DART train in a tunnel 80 feet beneath the the Knox-Henderson area of Dallas. A planned underground station to serve the neighborhood was started but never completed after residents strongly objected. (Jae S. Lee / Staff Photographer)

Back in the 1990s, when the underground transit line was constructed, there was supposed to be a stop here providing easy access to Dickey's Barbecue, shopping along Knox Street and a ride to work for folks that live in adjoining neighborhoods in East Dallas and Highland Park.

But vocal homeowners rallied against the transit line and raised a ruckus, so DART decided not to complete the station.

"It was part of our original plan, but there wasn't a lot of interest by the community, and unfortunately it was never used, said DART spokesman Gordon Shattles, who was along for Friday's visit to the abandoned chamber.

The rough-hewn cavern runs along the side of the train tunnel, walled off from passing trains with cinder blocks.

It's a jump of two or three feet down into the hole, where hundreds of passengers a day were supposed to board trains headed to Plano, downtown Dallas and beyond.

The last estimate I had of what it would cost to build the Knox Station was more than 20 years ago when DART representatives said would be more than $15 million and $20 million to complete the construction.

That's not likely unless some real estate developer with a big purse decides to foot the bill for the project.

Every day thousands of commuters rocket through these tunnels in trains going 60-plus miles per hour. But, except for the DART workers who spend their days maintaining the underground system, few folks have the opportunity to see what lies below the busy freeway.

There's a lot more than just the train tunnels.

Pedestrians passing over steel plates in the sidewalk along Willis Avenue at Central Expressway might not realize that they're actually trap doors leading to a subterranean section of DART's light rail system only used by maintenance crews and as an evacuation route in case of emergency. DART mechanics Amos Hargrove (left) and Bill Lakes shut the doors after giving DMN real estate editor Steve Brown and two photographers a tour. (Jae S. Lee / Staff Photographer)

DART chief rail operations controller Javier Molina and the self-described "tunnel rats" — mechanics Amos Hargrove and Bill Lakes — gave three of us from The Dallas Morning News a rare tour of this underworld.

The trip started at a metal trap door on the freeway frontage road and what seemed like miles of dark concrete steps going down, down, down to the rail line. Water drips into the passage, creating pencil-thin stalactites that dangle from the ceiling and patches of moss on the walkway.

"There are a lot of underground streams that seep through the walls," Molina said. "There are sump pumps to get it out."

Mechanic Bill Lakes (right) leads the way, followed by DMN real estate editor Steve Brown and Javier Molina, DART's interim technical administrator, down several flights of stairs to the unfinished Knox Street light rail station 80 feet below North Central Expressway. (Jae S. Lee / Staff Photographer)

The air down there is hot, humid and fetid — even at the lowest levels.

Wind from a passing train brings brief relief and a warning to hold on to the tunnel side railing while the cars passes.

"The trains going through the tunnels push air in and out," Molina said.

1 / 3A DART train whizzes past a maintenance tunnel near the unfinished Knox Street station 80 feet below Central Expressway.(Jae S. Lee / Staff Photographer) 2 / 3Javier Molina, DART's interim technical administrator, watches from a maintenance tunnel as a train passes. What was intended to be an underground station to serve the Knox-Henderson neighborhood now serves as access for workers and as an emergency exit route.(Jae S. Lee / Staff Photographer) 3 / 3A DART train bound for Dallas-Fort Worth International Airport passes through a tunnel near the unfinished Knox Street station 80 feet below Central Expressway.(Jae S. Lee / Staff Photographer)

There are separate north and southbound train tunnels. Running between them are 21 corridors with metal doors.

"If a train broke down or there was a fire, we could evacuate people through those tunnels," Molina said.

Near the Knox Street station is a titanic underground vault with exhaust fans the size of a school bus. The fan system can pull all the air or smoke out of the train tunnels in a matter of minutes if needed, exhausting it up a huge shaft that runs to the surface.

Rows of yellow caution signs warn people not to go into the room when those hurricane force fans are running.

"Leave ventilation shaft area immediately when horn sounds," the display warns.

1 / 7From left: Gordon Shattles, DART external relations director; DMN real estate editor Steve Brown; DART mechanic Amos Hargrove; and Javier Molina, DART's interim technical administrator; explore an underground ventilation fan room near the unfinished Knox Street underground rail station. Exhaust fans the size of a school bus can quickly clear the tunnels of contaminated air or smoke if needed.(Jae S. Lee / Staff Photographer) 2 / 7Warning signs about as mechanic Amos Hargrove opens a door to the fan room inside the DART's underground tunnel in Dallas, Friday, July 20, 2018.(Jae S. Lee / Staff Photographer) 3 / 7An emergency phone and directions to the nearest exit, seen inside DART's underground tunnel system in Dallas, Friday, July 20, 2018.(Jae S. Lee / Staff Photographer) 4 / 7Past visitors wrote on the wall in the fan room inside the DART's underground tunnel in Dallas, Friday, July 20, 2018.(Jae S. Lee / Staff Photographer) 5 / 7An exit sign to the stairwell is seen on a door inside a DART's underground tunnel in Dallas, Friday, July 20, 2018.(Jae S. Lee / Staff Photographer) 6 / 7A giant ventilation shaft rises to the surface from deep inside DART's underground tunnel in Dallas, Friday, July 20, 2018. (Jae S. Lee / Staff Photographer) 7 / 7The covering of the ventilation shaft to DART's underground tunnel at the corner of Central Expressway and Willis Avenue in Dallas, Friday, July 20, 2018.(Jae S. Lee / Staff Photographer)

I was ready to climb back eight stories of stairs to get to the surface.

The next time I want to see that tunnel, I'll take the train.