Peter Woodall's favorite places in Philadelphia are the buildings most people drive by.

Take an abandoned factory on North Broad Street that's been turned into loft apartments. Untouched by a modernizing city, the old machinery was left to collect dust, and a sign stayed for years on the wall warning the long-gone workers that they weren't allowed to take any work home when they left for the day. Pinups from another era hung in the locker rooms.

"It's the places that were abandoned that you can imagine what might have happened. It's incredible to get a glimpse of that," Woodall said.

Woodall is the full-time director of tours and events for Hidden City Philadelphia, a nonprofit devoted to connecting Philadelphians to parts of the city they might otherwise have passed over, and educating the public about issues of building history. He also coedits Hidden City Daily, an online publication that covers not only preservation but city planning.

Hidden City began as a festival in 2009 that brought people into 10 spaces around the city and emphasized connecting them with art designed for the spaces. Hidden City put on another festival in 2013, but large events require years of planning: The organizers have to get permission from the owners of the spaces, connect with artists, get permits from the city, recruit volunteers, and raise money to pay for costs.

From that beginning, Hidden City began to morph into something that didn't depend on a festival. Now, the organization provides tours of sites around the city three to five times each month in addition to producing Hidden City Daily.

"It started out as an artistic problem: How to bring audiences to new work," Hidden City founder Thaddeus Squire said. "The art function of Hidden City has gone away."

Squire, 42, has stepped away from his work at Hidden City and is now the managing director at CultureWorks Greater Philadelphia, an organization he started in 2010 that does some management work for Hidden City.

The three main Hidden City figures - Woodall, Squire, and editorial director Nathaniel Popkin, who has written articles about architecture for The Inquirer - have often wondered whether Hidden City could be done somewhere else.

It could probably work, they agree, but there's something special about the way Philadelphia architecture has aged through the years. There hasn't been much "gentrification pressure" on most Philadelphia neighborhoods, which has left old buildings to age naturally, said Popkin, who specializes in writing about history and the city.

The city's relationship with its buildings has left Woodall, responsible for picking out places to use for Hidden City tours, with so many options that he's never afraid he'll run out.

"Ultimately, we want all these places restored. We hope the neighborhood improves, but the act of exploration is based on neglect," Woodall said. "If we were a healthier city, we wouldn't have so much to write about."

But Hidden City doesn't just tour places like Mount Moriah Cemetery - subject of a sold-out tour this month - or abandoned factories. A favorite tour of Woodall's is one that's called "Forgotten Chestnut Street." It covers five blocks, but it's led by a man who knows the history of every single building along on those five blocks.

Despite its unique place in the city discourse, Hidden City faces the same challenges as many other organizations. Popkin works like any other news director to find a niche for the Daily. He's found it, he says, in not just writing about places with history, but places with conflict.

"We make sure we're always bringing smart context to stories about today," he said. "We're not a history website or blog, we're very much anchored in the present day."

Woodall, despite his background in journalism, found himself drawn to the financial side of Hidden City.

Hidden City offers memberships, he said, and currently has about 400 members. Members get first option at the novelty tours that only occur once a year. Hidden City does an online fund-raising campaign annually and sells merchandise on its website.

He thinks Hidden City has a special appeal to Philadelphia's younger residents who want to discover the past outside of textbooks or a museum.

"There's something wonderful about finding it yourself," he said.

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