In the subterranean shadows, the models scurry at the sound of people tromping their way. They won't say why they chose this abandoned SEPTA tunnel for a fashion shoot, though the cavernous space does offer a darkly glamorous backdrop.
Above them, traffic zooms by on Pennsylvania Avenue, just steps from the Art Museum. The noise of cars and trucks barely penetrates the thick walls of the passage.
On this particular Saturday, a group of about 40 people were drawn here - armed with flashlights to avoid rocks and empty soda bottles in the blackness - by Paul vanMeter, a hyperkinetic professional gardener.
VanMeter has reimagined the remnants of the Philadelphia & Reading Railway as a path where pedestrians and cyclists (and maybe even fashion models) could travel without ever crossing a street.
"We are looking at Philadelphia's next great civic space," vanMeter said, as he and SEPTA officials led the tour along the path of the old tracks.
The trip began near Girard Avenue, wandered through the 52-foot-wide tunnel, burst into sunlight near the Rodin Museum, and continued through the Whole Foods parking garage before resurfacing near 20th Street.
From there, the group walked at street level, looking down at part of the trail that is not currently accessible and that runs under The Inquirer and Daily News building, before crossing Broad Street and heading to the old Reading Viaduct in the Loft District.
That section of the old train line already has garnered headlines as a proposed three-quarter-mile park similar to New York City's popular High Line.
Mayor Nutter has endorsed that proposal, and Alan Greenberger, his commerce director, and Paul Levy, chief executive of the Center City District, have been negotiating with Reading International to acquire the property.
Reading International officials were not available for comment, but Levy says they share the city's vision of "making it a great public park and stimulating renovation of a substantial number of vacant properties in that area. It's a real gap in the fabric of the city."
Levy is also working to expand housing in the area, especially as Chinatown spreads north. He and Sarah McEneaney and John Struble, who sparked the effort to turn the viaduct into an elevated park, have begun community planning and are hoping to have construction documents for a small portion of the new green space, known as the SEPTA spur, by the end of this year.
McEneaney and Struble have been working on the project for eight years. It's not clear whether the entire space will become a park, but recent funding from the William Penn Foundation and Poor Richard's Charitable Trust has propelled the idea forward.
Just two years ago, VanMeter and friend Liz Maillie dreamed up the plan for the old line's underground portion, which is known as the City Branch.
"You get this really neat soaring and submersive atmosphere," vanMeter said as he looked at the roughly 30-foot-high walls that surround much of the City Branch. He's calling the project ViaductGreene.
It is an urban ruin, overgrown with wild trees and plants. VanMeter believes it could be more than a wondrous city space - he thinks it can showcase Philadelphia's Industrial Age.
In the late 1800s and early 1900s, the train cars that once operated in the proposed park ferried materials to the old Baldwin Locomotive and other companies that clustered near the tracks.
"We want ViaductGreene to tell the story of the city's history," he said. "Right now, we're sort of stuck in tricorner-hat mode."
At this point, ViaductGreene is mostly a dream in vanMeter's head, but it does have one big backer. SEPTA owns the right-of-way and is eager to let someone else take care of it.
"If we can repurpose it as a sustainable asset," said Byron Comati, SEPTA's director of strategic planning and analysis, "it's actually more maintainable."
SEPTA would still own the property but lease it to a nonprofit to maintain it. While the transit agency may want to use the old line for trains again, Comati finds that unlikely - the tracks have been removed, and trains have not run there since the early 1990s. In the meantime, SEPTA workers must keep it clean, and the tunnel itself could become an expensive liability.
(Don't even think about going into the tunnel without SEPTA's permission. You will be trespassing.)
In addition to New York's High Line, other old railways have been turned into city parks and become popular attractions, including Promenade Plantee in Paris and Sudgelande in Berlin.
VanMeter estimates that turning the entire three-mile space into a park could cost $80 million, but he says the development could be done in stages, and so could the fund-raising. He and Maillie have started a nonprofit to take donations, and the project has become almost a full-time job for vanMeter.
Fund-raising is not the only challenge. There are the questions of how to keep a dark tunnel safe as a park and of how to get people, including those who can't walk, up and down from the street to the green space below. CSX still operates trains on a track close to the proposed entrance to the park on Girard Avenue, so designers would have to separate park users from train traffic.
VanMeter, 52, hopes to create a park that would retain much of the existing plant life to preserve the feel of a ruin and to control costs.
The site already offers a wide variety of perennials, including solidago, or goldenrod, Paulownia trees, and a lone Southern magnolia that has staked out a spot atop the viaduct.
"We like the idea of design through editing, as opposed to tons and tons of new planting," he said. He is bursting with ideas for what the park should look like, but one of his greatest hopes is to open up the planning to as many people as possible.
"We want to have an idea competition," he said, "let people dream about these places."
VanMeter, who grew up in Reading, is one of those people who easily sweeps others up in his dreams.
Peering through thick black glasses, he looks at a dull palette of brown plants, seemingly dead for the winter. "You should see this in summer!" he spouts. "It's crazy green!"
He still loves trains the way he did when he was a little boy. Standing atop the Reading Viaduct, he was moved nearly to tears at the possibility that the rails there could be sold for scrap.
Talking local history, he moves effortlessly from railroads to the Molly Maguires to the press baron Walter Annenberg.
And when his eyes travel up the walls of the old train line and alight on the Rodin Museum, it's easy to see what he sees: hundreds of Philadelphians and tourists walking and biking on the path, climbing up to the street to stroll along the Parkway and to dip in and out of the city's other treasures.
Tour the tunnels and the remnants of Philadelphia and Reading Railway at www.philly.com/viaductgreeneEndText
at 215-854-5520, firstname.lastname@example.org, or @miriamhill on Twitter.
For more information on vanMeter's vision, go to http://viaductgreene.org/2011/ 05/20/n-broad-viaductgreene/
ViaductGreene has been discussed by local photographer JJ Tiziou on his blog