Welcome to the netherworld.

Our guide for this tour of Atlanta's original underground is Jeff Morrison, a 34-year-old architect whose mild demeanor and bookish appearance conceal an almost goth fascination with spooky urban cellars. When he started working downtown, he'd take lunchtime strolls to explore the city's railroad history, most of which is hidden under viaducts and in dim recesses beyond the public spaces of MARTA, Philips Arena and Underground Atlanta.

"It took me weeks to find the Zero Mile Post," he says, referring to the chunk of granite that marks Atlanta's founding in 1837 as a rail junction called Terminus.

A couple of years ago, Morrison began leading invitation-only walking tours of the city beneath the streets. Part architecture, part archaeology, the excursions aren't always pleasant. There are occasional encounters with rats, rank smells and snarly security guards.

"This isn't going to be like the hidden cities you see on the History Channel," Morrison tells two dozen of us, gathered on a warm Saturday afternoon beside the steam engine outside Underground. "There won't be any dramatic music. There won't be any ghosts."

What he means is he doesn't tell ghost stories. There are plenty of ghosts in the realm where Atlanta was born.

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We begin by climbing the steps to Upper Alabama Street, where Morrison points out the railroad gulch that split downtown from its inception. Train traffic had grown so much by the early 1900s that the city considered building parks and plazas over the smoky canyon. It erected a network of bridges instead, creating the grottoes that would become Underground Atlanta.

"We won't go inside the mall very much," Morrison says dismissively. "There are a few things of interest in there if you look past the dollar stores and tarot card readers."

A block later, we ride an escalator into the mall to see one of those things: a gas streetlamp from the 1850s. During the Civil War, as the Union army bombarded Atlanta, a shell fragment ricocheted off the lamppost and struck a bystander. Solomon Luckie was not; he died of his wounds. One of the first victims of the siege, he was a free black man.

The lamp was relighted for the 1939 premiere of "Gone With the Wind" and rechristened "the Eternal Flame of the Confederacy." We read the plaque and consider the ironies as the Beach Boys' "Fun, Fun, Fun" plays from the mall speakers.

Stopped presses

We exit Underground across from the Five Points MARTA station and continue down Alabama Street past one of the saddest sights in downtown Atlanta: the decaying shell of the long-abandoned Atlanta Constitution building.

It pains Morrison. The Tulane-trained architect works at Robert and Co., the firm that designed the structure in 1947. Leading the group onto a pedestrian bridge, he points out the curvy lines and horizontal bands, still attractive despite the trees sprouting from the roof.

"It looks like an ocean liner, doesn't it?" he says. "That's one of the few Streamline Moderne buildings in Atlanta."

The Constitution occupied the complex for only three years, until it moved in with its new owner, the Journal. Now, to the distress of preservationists like Morrison, the authorities want to tear down the building and replace it with a new multimodal bus and commuter train station.

The rails giveth and the rails taketh away.

Vanishing railroads

We climb the stairs to the Spring Street viaduct and approach the Richard B. Russell Federal Building, the 26-story mediocrity that replaced Atlanta's greatest train cathedral, Terminal Station.

Both of Atlanta's downtown depots were demolished in 1972, a couple of years before the city began to learn the value of grand old buildings when the Fox Theatre was threatened.

Union Station, with its columned, classical facade, stood on Forsyth Street, so close to the newspapers that old-time reporters remembered cinders from locomotives drifting through the open windows and igniting copy paper. The only remnant is a weedy stretch of the loading platform.

Terminal Station, which looked like an Italian villa, with its twin towers and red-tiled roof, left more ghosts. As we stand on the viaduct, Morrison points to a couple of them. In a parking lot below, we can see the concentric pattern of rails that once fanned out from the station and still show through the asphalt that was poured over them.

Farther along, he directs our attention to the Interlocking Tower, an abandoned two-story building in the middle of the rail yards that was the station's equivalent of a flight control tower.

"It's got the same red-tile roof ... " Morrison begins. He says something else, but we can't hear it. A northbound freight is bellowing down the tracks.

Murky light, magnolias

We leave the viaducts near Philips Arena and descend long stairs to what might be called New Underground Atlanta. This is the lowest part of the tour, the underside of the parking garages and service roads that were built in recent decades for Philips, the Georgia Dome and the Georgia World Congress Center.

As we walk along the dark alley that used to be Magnolia Street, one of the group, Rob Hill, a real estate man in Sandy Springs, asks if anyone knows what stood here more than a century ago.

It seems that one of the men involved in the Great Locomotive Chase lived on this spot.

William Allen Fuller was the conductor who chased the train stolen by Union spies during the Civil War —- the fellow on the handcart played by Buster Keaton in the silent film classic "The General."

"Fuller had a house right here with two magnolia trees in the yard," Hill says. "He was proud of those magnolias."

Trees seem hard to imagine as we look up at six levels of parking and a thin shaft of sunlight.

The earth moved

Morrison believes there are only two landmarks in downtown Atlanta that predate the Civil War: the gas streetlamp and the Zero Mile Post. He used to say there was a third, but it doesn't amount to much anymore.

We emerge from the underground and come to a stack of rusty rails that have been pulled up in recent years. The rails ran along the Monroe Embankment, an earthwork built in the 1840s for one of Atlanta's first lines.

"There isn't much to see now," Morrison apologizes, explaining that the line was moved and the embankment leveled to fill nearby ground now used for parking.

Someone brushes the rust off one of the rails and discovers a year stamped on it: 1942. He snaps a photo.

A city's birthstone

We're in luck. The cops left the door unlocked.

The Zero Mile Post, erected before the Civil War to mark the spot of Atlanta's founding, is tough to find. For three-quarters of a century, the marker stood in the open beside the rail line to Decatur. In 1929, it was covered by the Central Avenue viaduct. In the 1980s, the state enclosed it within a depot built for the New Georgia Railroad.

Alas, the tourist train was short-lived. Today the depot is used by the Capitol police. There's nothing outside the redbrick structure to indicate the landmark inside. Sometimes the doors are locked when Morrison stops by, leaving tour members to press their noses against the glass.

We enter the building, pass a wall of wanted posters and come face to face with the milepost. The rough-surfaced granite marker stands barely 3 feet tall and bears a faint carving that reads, "W&A RR 00." Translation: Western & Atlantic Railroad, 0 miles.

This homely stone was the starting point for Atlanta —- the acorn from which everything grew.

"I wonder," Morrison says, "how many people even know it's here."

 Watercolor paintings by WALTER CUMMING / Staff
Graphic includes a map of downtown Atlanta and traces the above-ground tour and the underground tour, and locates Union Station, Terminal Station, gas lamp and the Zero Mile Post.
Graphic includes watercolors of Union Station, 1930-1972; Terminal Station, 1905-1972; and the gas lamp in Underground Atlanta.