There's much speculation as to what has stopped a giant machine boring a tunnel beneath downtown Seattle. Theories range from a man-made object from Seattle's past, such as a steam engine, to something from the natural world, such as a glacial boulder. NBC's Joe Fryer reports.

SEATTLE — In a city known for a giant needle pointing toward space, everyone is talking about a massive machine stuck underground.

They call her Bertha, a 57-foot-wide, earth-eating tunnel maker chewing her way below downtown Seattle to make way for an underground highway along the city's waterfront.

But two weeks ago, a thousand feet into her near two-mile journey, Bertha came to a grinding halt.

"We're a bit puzzled about what's preventing us from moving forward," said Chris Dixon with Seattle Tunnel Partners.

Officially, Bertha was stopped “after unanticipated and increasing resistance was experienced, possibly due to an obstruction.”

A mysterious obstruction, 60 feet down, and Seattle is abuzz with theories of what's in Bertha's way.

“There’s history buried everywhere,” local historian Feliks Banel said.

"It could be Jimmy Hoffa, it might be Sasquatch or it could be a flying saucer, you know."

The area where the machine currently sits, stuck, was once under water. The object blocking Bertha's path may be a remnant of Seattle’s industrial roots, Lorraine McConaghy, a historian with Seattle’s Museum of History and Industry said. The mid-1800s saw the construction of a major steam-powered sawmill in the area, and open water surrounding the mill was a dumping ground.

Historian Lorraine McConaghy on the mystery and excitement surrounding what may be blocking the progress of boring a tunnel and how it captivated Seattle.

“It could be just about any industrial artifact you can imagine that might have ended up in the water,” McConaghy said, adding the possibilities included a locomotive or boilers and engines used in the old mill.

Laura Harper, a history teacher from Yakima, Wash., echoed the theory.

"I'm assuming there's probably an underground building, a ship, some sort of artifact from maybe 100 or 200 years ago,” she said.

Seattle Tunnel Partners is taking steps to identify and remove the object, drilling 10 wells that will lower the water pressure underground so workers can safely get a closer look at what’s stopping Bertha. The process could take two weeks or longer.

Until then, Bertha remains stuck in place.

"There's thousands of guesses what's going on, but until we get down there and see what the actual situation is, it's just speculation and guesses," Dixon told a news conference last week.

Banel said that while the truth could turn out to be boring (read: It's just a big boulder), the mystery has provided an opportunity to reflect on the city’s past.

“If this delay in the tunnel project means more people are thinking about our local history, I think that's fabulous,” he said.

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