When it was first discovered, the museum director, Phillip Nord said it looked like an old mine, even a gold mine!
Of course, it wasn't, but it could still pay off for the museum.
Nord told Action News it is actually something called a Gas House, because it used to house an Acetylene gas unit.
"It provided acetylene gas that was piped into the mansion for their gas light fixtures," Nord said. "This gas could produce a very bright light that was better than coal gas."
There is documentation to support the find, saying that acetylene powered lights in the mansion around 1905. That wasn't a type of fuel just anyone could afford.
"You had to have a lot of money to have this. It was a very interesting, very dangerous system," Nord said.
The danger came from the volatility of the gas. It was so volitile, entire systems exploded.
So why are they so excited about the find at the museum? While it's no gold mine, and it isn't going to explode now, it could still propel the museum to a whole new level.
Nord said it could put Rockwood onto the National Register of Historic Landmarks, which would unlock some federal funding. In addition, he is exploring the possibility of something called a special Chemical Landmark designation. That seems to be a real possibility too, because the site where the inventor of the Gas House process worked, already holds that status
The Gas House was the main attraction at a recent event announcing a $1,000.00 donation for its restoration, from the Eastern Brandywine Hundred Coordinating Counsel.
The Gas House may be open to the public in about three months, and Nord is excited. "Some visitors have told us that the museum is the best kept secret in Delaware. I want to change that to the best historic house museum in Delaware."
Learn more about the Rockwood Mansion Museum