BISMARCK, N.D. (AP) — Locals are trying to find a way to repair and restore North Dakota's only railroad tunnel, built a century ago.

The Cartwright Tunnel and adjoining Fairview Lift Bridge comprise a walking path in the Yellowstone River Valley. They sit along a former Great Northern Railroad line in western North Dakota, not far from the state's border with Montana.

An engineering survey estimated repairing the tunnel's trouble spots would cost around $500,000, The Bismarck Tribune reported . Fairview, Montana, Chamber of Commerce President Ray Trumpower said his group is interested in repairing the tunnel, but it's cost-prohibitive.

The chamber installed caution signs for walkers along the tunnel's entry points. The site is close to Sundheim Park on the Yellowstone River and attracts many visitors.

"It's a very popular site and we would hate to see where it would ever come to a point where it would have to be closed to the public," said chamber member Kerry Finsaas.

Locals have called for fundraisers to fix the tunnel, but Trumpower said that won't raise enough money.

Trumpower said it may require a generous donor to take on the repair. He said the other option of imploding or sealing the tunnel may be impossible.

"It's too substantial a structure," said Trumpower. "To seal both ends off, it's tough and expensive to do."

"We're just going to keep working at it," Trumpower said.

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Information from: Bismarck Tribune, http://www.bismarcktribune.com