Two hours behind schedule, Beth Heinly finally located a working electrical outlet in the echoing cavern of the Broad Street concourse and settled in, wearing a puffy chef's hat, to cook pasta.

The mac-and-cheese giveaway was Heinly's take on site-specific performance art - meant to engage a space that mostly lies vacant, except for occasional skateboarders, scuttling rainy-day commuters, and covert smokers of marijuana.

"I wanted to do a really loving thing in a scary place," she said.

It was part of the second Open Call Guerrilla Outdoor Performance Festival, which is urging artists to explore this realm that sits just below the busiest parts of Center City, but, for the most part, outside the public consciousness.

Heinly organized the festival that ran last Saturday and this Saturday and includes 22 performances by 16 artists (find a map and schedule at ocgopf.tumblr.com).

It was timely, considering that the concourses - which span 3.5 miles, beneath Market Street between Eighth and 18th Streets, and below Broad Street from Market to Locust - are poised for a makeover.

SEPTA took control of the corridors from the city in July. And, unlike the city, it now has funds to improve them, thanks to a state transportation-funding package passed in 2014. For the first time in years, officials seem excited about the potential.

"It's a great asset of this city that's been long underutilized," said Joseph Palantino, senior director of capital construction at SEPTA, which budgeted $54.5 million for upgrades.

It has already begun repairing flooring that has cracked due to years of leaks, and improving signage. Next, it will replace key escalators and elevators, clean up stairwells, and upgrade the lighting and finishes in the passageways.

It's even embarking on creating a master plan that could incorporate big ideas for reusing the large, vacant spaces, and will be seeking public input, said Robert Lund, an assistant general manager.

It's a space that has, for decades, inspired imaginations, but also foiled hopes. (It has also been a source of urban myths. Jerry Kaba, who on Saturday spent two hours down there playing chess in a hazmat suit and gas mask as part of the guerrilla festival, was inspired by rumors that it was built as a fallout shelter.)

The passages were built over decades, beginning in the early 20th century, alongside new subway lines.

Harris Steinberg, of Drexel University's Lindy Institute for Urban Innovation, described them as relics from the optimistic era, when Philadelphia's population was growing. They represented an important part of planner Edmund Bacon's vision of an underground city where pedestrians could be separated from car traffic.

Steinberg remembers their feeling safe and well-used into the 1970s.

"It was a lot more porous," he said. "You could get in and out of buildings, like Wanamakers and the Ritz, and there was a lot more life down there."

But by the 1990s, they'd become host to an underground shantytown for more than 350 homeless. (They were cleared out for the Convention Center's opening in 1993.)

Today, the space still shelters many homeless people and provides cover for illegal activities. Last year, The Inquirer reported that it took 11 cleaners working morning and evening shifts to keep up with the "human waste, cardboard beds, condoms, and needles."

Yet, for many, these are spaces with irresistible promise.

"I don't know how many undergraduate and graduate-school projects on activating the concourse there have been - probably dozens over the years," said Andrew Stober, chief of staff at the Mayor's Office of Transportation and Utilities. "A lot of those ideas are on the table."

For some examples, we turned to a few architects and planners already transforming some of Philadelphia's other underutilized spaces.

Bryan Hanes, the landscape architect who is designing Philly's planned Rail Park, has considered segments of the concourse for a range of public and private clients over the years. He has also asked his students, who attend Penn State but study urban design in Philadelphia, for their ideas.

"The conclusion is," he said, "there are great opportunities for all kinds of things."

Some ideas he has investigated include bicycle storage, bike-share stations, bike-repair shops, and even bike lanes, all of which would be fitting for a transit hub. (Another is public showers, perhaps for all those sweaty cyclists.)

He has considered what kind of skylights would work in the space and how to bring Avenue of the Arts stakeholders down there, through art galleries or performances.

"We've talked about it from the perspective of an event space: Could there be underground parties, dances, film screenings, and art exhibitions?" he said. "We've talked about it from a culinary perspective. It's dark and dank down there. Could you have a mushroom farm or a wine cellar? We've looked at it from an environmental perspective: There's opportunities to collect and store massive amounts of storm water."

Stefan Al, an architect and urban design professor at University of Pennsylvania, sees retail - and the street life that brings - as key to reviving such a space. He points to bustling concourses in Hong Kong as an exemplar. There, he said, retail not only brings the safety of "eyes on the street," but also provides crucial revenue to the transit agency.

"These walkways are really part of the public realm. People use them a lot," he said, "and they're not just places to get from A to B, which is kind of the problem right now."

Bringing all of that to, say, the Broad Street concourse would require a significant investment, because there are limited utilities there, Stober said.

But infrastructure can be improved. Attracting the foot traffic that will, in turn, attract those retailers may be more difficult.

It's not impossible, said David Fierabend, whose Groundswell Design Group in Mercer County has become known for turning forgotten spaces into trendy pop-up destinations.

"Short-term activation is really necessary to create that energy," he said. "And this space has great history to it, it's sexy, and it also has a purpose."

He's thinking aeroponic gardens, hanging from the ceiling or covering the tiled walls, or plantings irrigated by storm-water collective from above, suggesting an underground park.

"The greening element would make the biggest change," he said, "and make it more of a destination."

He could envision lighting installations tied to the movements of trains or changes in sunlight outside - or perhaps a tunnel planetarium. Why not a linear coffee shop, or a cocktail bar evoking a speakeasy?

SEPTA is willing to consider almost anything, Lund said on a recent walk-through. Looking past buckets catching leaks and the cracks in the floor, he envisions restoring life to the blacked-out, department-store display windows lining Broad and Market Streets.

"We've talked about an indoor park or a walking track down here, or pop-up gardens," he said. He'd like to attract the type of people who might otherwise be mall-walkers, or to work with the Kimmel Center and University of the Arts to bring performances downstairs.

Still, Steinberg warned that, although there's no shortage of ideas for the concourse, there's a question of whether downtown density can support it.

"Everything you put underground takes away life from aboveground. The Gallery killed East Market Street," he said.

But now that the East Market development and Gallery overhaul are underway, perhaps the concourses' time has come, he said. The key is, "you want life aboveground first." 

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