Installation by Ben Neiditz and Zach Webber at Fort Mifflin in Philadelphia (photograph by Allison Meier)

Places tend to be forgotten when their function disappears, and there's no reason to engage with their space. The Hidden City Festival in Philadelphia, happening through June 30, is not just opening nine overlooked sites, many which have been abandoned or long locked to the public, but initiating new experiences to connect people to these lost locations.

The six-week festival launched in 2009 and returned this year, although Hidden City has a web magazine and tours throughout the year in unexpected places all over Philadelphia. Atlas Obscura took a field trip down to the festival last week to explore some of the 2013 sites, and their forgotten history. 

FORT MIFFLIN AND MUD ISLAND

Cabin in the woods (photograph by Allison Meier)

Fort Mifflin on Mud Island dates back to the Revolutionary War, although it was totally wrecked by the British in 1777 in an attack that had a rate of a thousand cannonballs falling an hour onto the fort. However, it was rebuilt over the years, and even if Mud Island isn't much of an island anymore with the airport and other development, it still feels wild with overgrowth and an abundance of birds. 

For Hidden City, area artists Ben Neiditz and Zach Webber built tree houses, cabins, and other secrets to discover in the forested area just outside the fort on the Delaware River. It had something of the wish fulfillment of childhood, with the structures you'd imagine built from scraps of wood realized (with better structural integrity), and the discovery of getting lost in a strange woods. In one area there was a creepy cabin filled with twigs, and in a dark tunnel two skeletal figures twined from twigs sat in dark corners waiting to be discovered by flashlights. We probably missed some things in the dense area, but at the summit of the hill was an unmissable view from a small house with a parapet looking to the city skyline. 

Experiencing the tree house (photograph by Dylan Thuras)

View from the tree house (photograph by Allison Meier)

Lurking twig figure (photograph by Allison Meier)

Bridge over washed-up trash (photograph by Allison Meier)

Grass shelter, which had a floor of shells (photograph by Allison Meier)

Tree house hiding in the trees (photograph by Allison Meier)

SHIVTEI YESHURO-EZRAS ISRAEL

 Storefront synagogue (photograph by Allison Meier)

The Shivtei Yeshuron-Ezras Israel storefront synagogue was once a thriving part of the large Jewish community in South Philadelphia, but as that local community moved to other parts of the city, so did the congregation dwindle until it could be counted on one hand. Now Hidden City is including it to get attention to its over a hundred year history, which goes back to its establishment in 1909. The festival is hosting a "Radical Jewish Music" series there, and on the second floor is the ADMK Knit Lab, where participants can help knit a giant quilt to cover the whole front of the building.  

Historic memorial lights with plaques in Hebrew (photograph by Dylan Thuras)

View from a door that opened up on the second floor, where women would once attend the service (photograph by Allison Meier)

Banner in the synagogue (photograph by Allison Meier)

Tenement at the top of the building, where visiting rabbis would stay (photograph by Allison Meier)

ATHENAEUM

The Athenaeum (photograph by Allison Meier)

The idea of Athenaeums, which were association-based lending libraries, has almost entirely disappeared, but Philadelphia's has been operated since 1814. It doesn't look like much from the outside on Washington Square, but the interior is an absolutely gorgeous space in an elaborate Italianate Revival style. The two floors of bookcases in the library have glass doors, and there's even an old drinking fountain where water was filtered through a stone. 

In the chess room for the Hidden City Festival, artist Ruth Scott Blackson is presenting her project on the home of Edgar Allan Poe, all based on a curious book she came across at the Athenaeum that described the details of Poe's Seventh Street house with only text, no images. Using a variety of sources, from a vintage color wheel to a dictionary of every word of Poe's writing, she made her own books recreating the colors of each room with lines of his poetry and stories. 

Guest book for the Athenaeum, with Poe stopping by on November 19, 1838 (photograph by Dylan Thuras)