When Lauren Gunderman, 31, and her partner bought a historic church in upstate New York, they knew they were taking on an ambitious renovation project.

The former Presbyterian church in Waterville was built in 1872, and the couple planned to transform it into a luxury wedding and events venue. But somewhere between the old walls, high ceilings and decades of renovations, they spotted something that did not seem to make sense.

Two windows on the outside of the church appeared to belong to a room that did not exist inside.

That strange mismatch soon became a mystery that drew millions of people into the couple's renovation journey.

The mystery soon spilled onto social media. On May 25, Gunderman and her partner shared a video on their Instagram account, @127eastmain, inviting viewers to help solve the puzzle. In the clip, they attempted to reach what they called the "mystery room" by removing boards from the ceiling beneath the area where they believed it might be hidden.

(Courtesy of Lauren Gunderman/@127eastmain)

"How the hell we get into this mystery room?" the post says in the video.

The couple had noticed the two exterior windows but could not find a corresponding room inside the building. There had to be something behind them — or so it seemed.

They searched for an entry point and eventually found a small opening beneath the suspected location. It had been boarded over, raising hopes they had finally discovered the way in.

But old buildings, as anyone who has ever renovated one knows, are not always eager to give up their secrets.

After removing the boards, the pair lowered a phone into the space to investigate. Instead of a hidden chamber, forgotten staircase or dusty time capsule, they found more structure.

And more floor.

"In this video, we're trying to locate the 'mystery room,' which is wherever those two windows you see on the exterior actually exist inside the church," Gunderman told Newsweek. "We figured going through the floor would get us there, but instead we just found ... more floor."

Her Instagram caption added a lighter note to the frustrating search: "Another attempt at getting into the mystery room in my 1872 church! Why am I wearing pink slides with socks?"

The video quickly became a hit, drawing more than 4.9 million views and more than 137,000 likes, according to Newsweek. As viewers watched the couple climb ladders, pull away boards and try to solve the puzzle, the comment section turned into a mix of amateur detective work and horror-movie warnings.

One commenter wrote that the couple had bought "an old church with a boarded off room" and immediately wanted to know how to get inside, adding that it sounded like "where the demon sleep."

Another viewer had a simpler recommendation: Don't open it.

"Old church, boarded up room, yep I'm not opening that up!" the commenter wrote.

Others urged the couple to leave the sealed space alone — or at least have the church blessed first.

But amid the jokes about demons and haunted rooms, some viewers offered something more useful: possible answers.

Although the couple has not managed to access the suspected room, Gunderman told Newsweek that comments from organ experts may have helped explain the mysterious windows.

"Spoiler: after receiving a flood of comments from organ experts, I've since learned the windows were likely boarded up inside the organ room after it was electrified, but I don't want to mess with the pipes, so we may never know for sure!" she said.

For now, the old church is holding on to at least part of its secret.

The explanation may be practical rather than paranormal. Still, the mystery has given the couple's renovation a story few first-time property owners could expect: two windows, a space that seems to be missing, millions of curious viewers and a historic building that may not be ready to reveal everything just yet.

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