Something like this will definitely raise the value of a house.

An Illinois man recently discovered a large, manmade tunnel hidden underneath his house. According to experts, the structure dates back to the 1800s and possibly played a significant part in history.

Gary Machens, of Alton, Ill., had no idea that the tunnel was sitting underneath his house until he had to repair the sidewalk, Fox 2 Now reports. According to him, the sidewalk had started to slope and he needed to excavate and repack the area.

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He described the tunnel to the news outlet, saying, "So, it was at least 9 feet tall. We’re standing on about a foot of dirt and it’s 9 feet wide and how far back it goes, we don’t know. We know it goes back 60 feet."

Machens says that according to local historians, the tunnel was built around 1840, 50 years before the house above it was built. As for the purpose of the tunnel, that apparently remains a mystery.

"It’s unique, there are a few tunnels around the Alton area since we checked with the Landmark Historic Society," Machen said. "It’s been used as an icehouse or root cellar or a lot of other options.

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Some people have also theorized that the tunnel may have played an important part in the nation’s history.

"It could have been used for the Underground Railroad," Machens explained. "There’s no proof of that but there was a ferry here in the Alton area to the Missouri side and it’s possible it could have been used for that."

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Apparently, the house that currently sits on the property has a rich history in the area.

Machens said, "Yes, three former mayors of Alton have lived in this house through the years. I don’t know if any of them knew about this. The house was built in 1890, the tunnel is believed from 1840, so it was here for 50 years. What it was used for, I don’t know. We’ve got maps that go back to 1863 and this house was not there and there was not another house on this property here."