If you're bragging about Philadelphia and its unique charms, be sure to add the upcoming Hidden City Festival to the list. This is something nowhere else has -- it's ours and it's amazing.

The first iteration took place in 2009, when founder Thaddeus Squire and his team opened up some of the city's inaccessible architectural gems to the public. They transformed those abandoned and underused spaces into canvases for art installations and performances. Over 10,000 people showed up to explore the sites, which included the Metropolitan Opera House, the Royal Theater, Shiloh Baptist Church and Disston Saw Works.

Round two for the festival has been years in the making. This time they're doing things a little differently, focusing more on interactivity and community. The five-week-long extravaganza -- kicking off May 23 -- will feature nine sites, with opportunities to meet the artists, docent tours, walks, concerts and discussions. A variety of passes (daily, weekend, festival-long) are available; Thursdays are free.

Flying Kite sat down with Tusman to talk about what makes the Hidden City Festival so special.

How does this year's festival differ from the 2009 incarnation?
The first year, the art was about the space -- it was informed by what had happened there, taking the form of contemporary art, sculpture, installation, painting, quilts, things like that. This [time], it's what they call "social practice art" -- socially interactive art projects that could be, say, a temporary bar set up inside the Kelly Natatorium site or a functioning citizens' town hall inside Germantown Town Hall. It's less art about a thing than art that is a thing. 

So the sites are more interactive?
When you go to a site, you can't really just look at it and walk away. You really have to get caught up in it. At least that's our hope.

Germantown Town Hall will be transformed into an Occupy-style town hall where the people themselves -- the Germantown residents and other visitors -- can make a flag, or they might discuss breaking away from the city of Philadelphia. There can be spontaneous performances and meetings. An archive or a radio station can pop up. And that's inspired by the site, which was built as a "town hall," but never used as one -- it was built right before [Germantown] was annexed by the city of Philadelphia. They had this money to spend, and spent it before the city could take it. 

And volunteers help run the sites?
Yes. So far, we have 150 volunteers; we're hoping for 300. There are some people who are interested in historic spaces, some who are going after adventure, others who love great art. And then there are people saying, "This spot is opening up in my neighborhood and I've never been inside. I want to see what's there." 

How did you choose the sites?
I grew up in Philadelphia, and these are all sites I had never visited growing up. Even as an adult, I had never been to these locations because they are off the map -- either closed to the public or generally not accessible to the larger community.

I think we often tell the story of colonial history in Philadelphia, but the story of industrial history is really not well-told. There is so much manufacturing space from the past -- and the present, frankly -- and its been really interesting to learn more about these spaces, figure out ways to get people into them, to report on them and see how they transform over time.

Globe Dye Works [in Frankford] is a good example -- it's a network of seven buildings, and they are slowly being turned into artist studios; there's also a coffee roaster. But then there's this huge abandoned boiler room right in the center. Steven and Billy Dufala are creating an installation.

Is the hope that, after the festival, some of the spaces will get new life?
That was more of an accident with the first festival, and that's more of an intention with the second festival. A good example is Shiloh Baptist Church. It's big. The congregation changed and it was very expensive to maintain. We presented some projects there, and now it's actually used as a site for performance. Those connections were made through the Hidden City Festival in 2009. 

How do people tend to experience the festival? Do most attendees visit more than one site?
In 2009, about 50 percent went to two or more sites, and a little less than 25 percent went to all the sites. The most visited site was Disston Saw Works, which was the furthest from Center City. So this time we didn't shy away from doing lots of projects far away from the center of the city. 

Any specific things you're excited about?
The site I just came from is the "Society Of Pythagoras," a secret society that's being created in Hawthorne Hall in West Philly. It was the site of secret fraternal organizations. There is stuff that I can't even tell you about. It's going to be amazing. I don't want to say! But if you can imagine secret bookshelves that lead to secret rooms -- that's all I'm going to say.

When you go to Fort Mifflin, there's a moat around it, and then there's a narrow strip of land and then the Delaware River. And to get to the artists' project -- which is called "Ruins at High Battery" -- you actually have to walk about 150 feet along this narrow causeway. When you get to the end of it, there's a wetlands environment. There are ruins of old magazine batteries where gun powder was stored -- it was an area that was actually taken over by the British during the Revolutionary War. Their project is scattered in the trees. There's a hidden beach. There's improvised settlements that the artists are building. It's a really amazing experience.

Shivtei Yeshuron-Ezras Israel Synagogue [in Pennsport] is over 100 years old. They have things from their whole history there -- like old signs from the '40s and '50s. On the third floor, there is a tenement apartment. It's interesting to trace that history of early Jewish immigration from the 1880s through the 1920s and '30s and actually see where it took place. That neighborhood has recent immigration too, from Southeast Asia. It's interesting to contrast that change over time. It's also a small house synagogue -- the last. There used to be up to 150 in that area. 

It's amazing that you are able to tackle such challenging spaces. For example, when Flying Kite was On the Ground in Germantown, we heard that Town Hall might be impossible to save. 
You know that phrase "too big to fail"? There are a lot of old buildings that are too big and costly to transform, but that's often because developers and architects have one way of thinking about things. That's why I work with artists. They're innovators. They're creative. They're flexible. They're financially creative, too. The idea of having a citizens' town hall would not come from a developer or architect. It will be amazing -- they might actually figure out a new solution for that space.

What we're doing is not very common -- temporary projects inside spaces that are very difficult to gain access to. We're doing very tactical urban projects. It turns out that just doing something and getting people into a space gets a dialogue going. And dialogue is sometimes enough to get things moving -- it's enough to save a roof, to get a community of docents together or to get someone to pay attention to the dynamics going on in a neighborhood.

The Hidden City Festival runs May 23 through June 30 at nine sites across the city. Visit the website for a complete listing of events. The Hidden City staff will also be blogging throughout the festival. Click here for tickets & passes; click here to volunteer.

LEE STABERT is managing editor of Flying Kite; follow her on Twitter @stabert.