It wasn't much to look at: a shadowy two-foot-tall opening, shored up by a few pieces of wood. Yet when that image flashed on the screen two weeks ago, the gathered crowd cheered.
"Everybody knew what this meant," said Sally Elk, executive director of the Eastern State Penitentiary Historic Site. "A lot of folk tales and stories were substantiated."
It was the escape tunnel running under the yard of Eastern State Penitentiary, the one that 12 inmates -- including legendary bank robber Willie Sutton -- used 60 years ago to find freedom, if only briefly.
The 97-foot-long shaft, which took almost two years to dig, stretches from a cell block to a spot outside the prison's stone walls.
To commemorate the anniversary of the April 3, 1945, escape, the nonprofit organization that runs the historic site is conducting a two-part archaeological excavation of the tunnel. In the spring, archaeologists uncovered the entrance and exit and found artifacts such as a nickel and a Sealtest milk bottle from 1945.
The second phase of the $19,000 project -- a quest to find the exact location of the length of the tunnel -- began last month.
Over the years, more than 25 escape tunnels were dug in the grounds of Eastern State -- none as famous as the one that was dug, buttressed with boards and wired for lights by cellmates Clarence Klinedinst and William Russell.
The pair did all the work, and 10 others, including Sutton, took advantage of it, entering the tunnel from the two men's cell, wiggling through the narrow space and emerging as dirty as sewer rats on the outside.
Freedom did not last long: Sutton was recaptured within minutes, five others within hours, and all were back behind bars less than two weeks later.
But the legends about the tunnel have lasted for decades.
"Everybody loves escape stories, even people who pay attention to the historical significance of the buildings and the noble intentions of prison reform," Elk said.
Archaeologists from John Milner Associates were brought in to handle the project. They knew the tunnel ran about 10 feet below ground but were unsure of its path. Although they do not plan to fully excavate the tunnel, they intend to photograph and videotape it. They would love to recover some of the electrical wiring or one of the light bulbs that guided the escapees.
"Even when you know something is underground, there's something about seeing it that's dramatic about it," archaeologist Rebecca Yamin said. "There's something about seeing that piece of the past that transports people back there that talking about it doesn't."
First, the searchers tried using ground-penetrating radar to pinpoint the tunnel, but something subterranean kept throwing off the signal. Then they bored two holes through the pavement in hopes of hitting the shaft so they could drop in a camera.
They found nothing.
"At the end of the first day, we thought the tunnel had just collapsed in on itself. We knew it was a possibility, but we were frustrated," Elk said.
On the second day, the workers drilled a third hole, this one close to the prison's outer wall. About 10 feet below ground, the boring tool hit open space.
"They came over and said, 'We found it! We found it!' " Elk said.
A camera dropped into the hole showed the wood still standing against the tunnel's sides. Further exploration planned for the winter months could yield more of the tunnel. At the least, Eastern State has another story to tell its visitors.
"I don't know of any prison museum that has a tunnel that's still there," Elk said. "It's fabulous."