It was meant to be a routine day of renovations at the former Carnegie Free Library of Allegheny building that is being transformed into the Children’s Museum of Pittsburgh‘s new Museum Lab.

But on Friday, as the construction crew tore down worn plaster to install a new front door at the Museum Lab, they spotted a mass of stone peeking out from behind the wall. Pulling away more pieces of plaster, they discovered a carved panel that seemed to be some kind of decorative element from the 1890s.

Photo courtesy of Children’s Museum of Pittsburgh.

“These moments are common during the process of revitalizing historic structures and are often unsettling,” says Chris Cieslak, the Children’s Museum’s project manager for Museum Lab. “The question always being, ‘Will this be a disappointing or wonderful discovery?'”

Photo courtesy of Children’s Museum of Pittsburgh.

As you can see from these photos, the discovery was pretty wonderful.

After cutting away a 5-by-8 section of the wall, they revealed what appears to be an enormous terracotta windscreen archway with gorgeous details. The construction crew continues to cut the wall away to reveal more of the archway structure, which was a common feature of buildings constructed in the late 19th century.

The 46,000-square-foot building, which will be home to the Museum Lab, had operated continuously from 1890 to 2006, but was forced to close after being struck by lightning. Friday’s surprise wasn’t the first beautiful discovery since redevelopment of the building began in early 2018: Crews have also uncovered five oil paintings hidden behind the walls, which are currently in storage.

“Discoveries like these are thrilling,” says Children’s Museum of Pittsburgh’s Executive Director Jane Werner. “We are now in the public phase of our fundraising campaign for the Museum Lab, and moments like this spotlight our need to raise additional dollars in order to both finish the project and capitalize on new discoveries like these.”

Learn more about Museum Lab here, and stay tuned for further coverage on this ambitious project.