At Hidden City Festival, forgotten bits of Phila.

A dozen or so people were climbing stairs and shuffling through corridors in the abandoned apartment house on Lancaster Avenue, but the atmosphere in Hawthorne Hall felt more like that of a cathedral.

For years, the building housed a theater used by fraternal organizations such as the Knights of Pythias and the Odd Fellows.

But for the last month, it has played host to an enormous, multi-room indoor art installation made of found objects - all part of the Hidden City Festival, which has curated installations at nine other abandoned or underused sites around the city.

Since the beginning of the month, a small army of volunteers and artists has been guiding visitors around the city - from an abandoned indoor swimming pool off Kelly Drive to Revolutionary War-era ruins at Fort Mifflin.

This was the last weekend of the festival - which was last held in 2009 and drew about 10,000 visitors. This year's iteration brought in even more, organizers said, although official attendance numbers were not yet available. But the success of this year's go-round was heartening for Hidden City, which has grown from the 2009 festival into a full-fledged organization that hosts tours and events year-round and publishes a daily online magazine.

"We're a hybrid. We're not a preservation organization or an arts organization," said Lee Tusman, Hidden City's creative director. "It's about new, innovative projects that bring new life into spaces that are either overlooked or vacant."

Inside Hawthorne House, visitors stood silently before an enormous wooden structure built over and around the stage on the second floor; snapped photos of a long dinner table set for dozens, tilting up to the ceiling; and ducked their heads to disappear into tiny cubicles beneath the stage crammed with ephemera.

"I didn't know there was an installation - it's not what I was expecting," said David Raphaely, an actor who stopped by Hawthorne Hall late Saturday afternoon. "I'm a history buff, so it's right up my alley. It's nice to know it's right in our backyard."

Across town at the abandoned Kelly Natatorium, beneath the Fairmount Water Works, a team of enthusiastic artists served iced tea and unveiled three boats they said were designed for different Philadelphia "futures" - to deal with the effects of climate change, fracking, and water privatization, respectively.

"[Turnout] has been amazing - especially on Saturdays, we've been slammed," said Elliott Montgomery, an artist from New York City who worked with a handful of other artists to create the boats over the last several weeks in the now-dry natatorium. "It's been a really nice way to see how people react to the chance that their imagined future could happen before their eyes."

At some spaces, such as the natatorium, Hawthorne Hall, and Fort Mifflin - where participants constructed makeshift homes among the ruins - artists were encouraged to graft their own work onto the abandoned sites. Elsewhere, participants are simply highlighting history that's already ingrained in the site. For example, at the John Grass Wood Turning Co. at Second and Race Streets, the owner abandoned the building in 2003 with nearly all its contents still inside.

Joe Klepka has been giving tours there each Saturday since the festival began. A wood-turner himself, he's been carving tops and handles for visitors while showing off some of the company's more archaic features.

"This is a swing saw," he said to a small group Saturday, pulling a positively medieval implement off the wall. "I know - it's like something out of a horror movie."

The workshop on Second Street, he said, is unique because it's still intact - machinery from the late 1800s is still gathering dust beneath the windows where Klepka began his tour Saturday.

Festival organizers said they were not sure whether they would host another festival. Tusman said obtaining the proper permits and ensuring sites are safe can be tricky.

But attendees said they were glad the festival was being held again.

"I missed the one four years ago - I was out of town - and really regretted it," said David Abraham, a law and economics professor at the University of Pennsylvania. "I've been waiting ever since."