Gary and Beth Arntson have had a lot of big ideas for their home. First, they wanted to build an earth-sheltered house. Then, a geodesic dome.

But after Gary scouted rural Goodhue County and came across a hill with scenic, sweeping views of the Sogn Valley, he knew what he needed to build atop the crest: a European-style castle, four-sided with towers on every corner, that would stand for 300 years.

In 1995, the Arntsons laid the first stone toward their dream castle, which they hoped would become a 6,000-square-foot bed and breakfast and wedding venue, as well as a grand living space for themselves.

More than 20 years later, the castle is partially completed, with one octagonal tower connected to 1½ sides. The courtyard that should lie in the center is just a snow-covered field used for parking.

Now in their 60s and hindered by illness, the Arntsons are walking away. The 6-acre property has been listed for sale since last spring. It's now under contract with prospective buyers, who have told the Arntsons they want to finish the castle.

"The project is not for the faint of heart," said Bradd Strelow, listing agent at Re/Max Cannon Realty. "It's big, and it's complex. It's not for just anybody."

Everything but the moat

The property would be easy to miss if not for the "For Sale" sign in the driveway. It's shrouded by trees, high on a limestone cliff above a sleepy county road near Cannon Falls. But once past a bend in the driveway, there's no missing what looks like a Bavarian country house that's been under construction since the Middle Ages. The only thing missing is the moat.

A crenellated parapet along the one completed side could easily be used for aiming arrows or cannons. The one completed tower is topped with a peaked black roof that the Arntsons call the "witch's peak."

This is Raven's Hill, so named because the Arntsons are fans of Ravenswood wine.

The idea for the castle was sown when Beth was 16. She visited Germany and became enamored of the fortified homes of European nobility. One Christmas years later, she bought Gary a book on castles, and the idea began to sprout.

In 1991, the Arntsons bought the land and let their imaginations run wild.

Gary drafted the plans with the help of an architect. He sourced 12-inch stone blocks from quarries in Minnesota, strengthened everything with steel, laid geothermal piping and sanded down the actual bedrock into a floor for the B&B's rooms.

Inside, copper piping is exposed — at least the stuff that hasn't been vandalized over the years. Wooden beams outline future walls to separate bedrooms. Staircases start and end, and doors seal off underground tunnels to nowhere. With angles everywhere, not one room is symmetrical.

"Yes, we are kind of insane," Gary said.

But Beth views their endeavor differently.

"My husband has a unique perspective and unique ability to see things," she said.

For 10 straight years, the pair "chipped away at it," Gary said. They fit in construction on nights and weekends, while working full time (Beth in human resources, Gary in trucking). Gary worked with masons on the castle tower walls' 45-degree angles, while Beth mined limestone from the hill and used it to make clay paths for a future formal garden. In winter, they'd burn a fire in a barrel to keep warm.

Finding regal antiques

Other times, they'd scour estate sales, collecting decorative antiques like swords and an ornate wooden coffer that would adorn the castle's lobby. Those items stock their South St. Paul home.

"We had a very long-term plan for this initially, not expecting that it was going to take us 20 years to even get moved in there," Beth said.

But over the past 10 years, their contributions to the project diminished while Gary dealt with physical ailments. Now retired, the idea of finishing the project and entering the hospitality field sounds too daunting, Beth said.

"It feels OK," said Beth about putting the Arntsons' dream to rest.

Still, the goodbye is tinged with disappointment. For years, they encountered people's "funny looks" when they told them about the project.

Then, they'd frustratingly have to update those people on the glacial pace.

"You move in your career from one job to another, or you run into somebody you haven't seen in a while who asks, 'Oh, are you living in the castle?' " Beth said.

"No, it's not done yet," was always their answer.

Now they have to tell those people the dream castle project, at least for them, is over.