Marsaw, 9, plays with a family cat Thursday outside the home of Curt and Deborah Sleeper in Festus, Mo. The sleepers have put the house, built in a cave, on eBay as a backup in case they can’t meet a large payment due on the property.

Festus, Mo. ? A lot of people are struggling to keep their homes in these tough economic times. One suburban St. Louis family is trying to keep its cave.

That is, a cave that’s also a home. Curt and Deborah Sleeper of Festus bought 3 acres of property and a cave in Festus in 2004, after they spotted it online. They fell in love with the unique geography of the old mining cave and figured out how to build a house inside of it.

But they’ve got a big payment coming due on the property and don’t think they can afford it. If they can’t secure new financing, they’ve got a backup plan — auctioning their cave home through eBay. Bidding starts at $300,000.

“I get the financing, or I sell the property, or I lose everything,” Curt Sleeper, a self-employed Web designer and small business consultant, said Thursday while giving a tour of the home.

Missouri has its share of homes built into the geography — houses built into the ground or in a hillside. The Sleepers’ home is unique even among them.

In the late 1800s, limestone mining created their bowl-shaped yard at the base of a hill. The 17,000 square foot cave where they live was hollowed out by sandstone mining through the 1930s.

Festus resident Sue Morris bought the cave in 1958. In 1960, she opened a roller rink there and hosted concerts, including shows by Ted Nugent and Bob Seger. The rink closed in 1985. A glass recycling center moved in until 1990, when the property switched hands between a private owner and then a realty team.

The Sleepers enlisted friends to help build the unique structure. A gray timber frame exterior was constructed in the 37-foot-tall opening of the cave. Thirty-seven sliding glass doors also are used as windows throughout the three-story, three-bedroom home, allowing natural light throughout the finished sections of the home.

Inside, the walls and ceiling are built from the natural cave stone. A huge umbrella is positioned above the living room furniture to catch grit that falls from the rock. Three large dehumidifiers keep the interior from getting too damp or musty. The family ran several tests to make sure the air quality was OK before moving in.

The home has electric, water and sewer, a decked-out kitchen and a whirlpool tub. It also has a goldfish pond.

Behind the living quarters sits a large cave chamber that serves mainly as storage.

Curt Sleeper said there are no bats in the cave, and no bugs beyond the normal stuff. “Nothing a cat or two won’t handle,” he wrote on a Web site.

One plus to living in a cave is climate control. The cave is at a constant 62 degrees. In fact, the home doesn’t even include a furnace or air conditioner.

Sleeper said he’d never want to own a traditional house after his time in the cave home.

“I’d never live in a box again,” he said.

The cave home sits alongside a working-class neighborhood just a few minutes away from the shopping centers and gas stations of Festus’ business district. The community of 11,000 residents is about 30 miles south of St. Louis.

After buying the cave, the Sleepers lived in tents inside of it as they spent about four years on the construction. The home was completed last year.

Sleeper said the family paid about half of the $160,000 purchase price for the cave up front. The seller agreed to allow them to pay the rest of the property costs after five years. They’ve also invested another $150,000 to build the home, he said.

But the balance of the purchase price is due in May, and the family doesn’t have the money. Sleeper said the seller has been generous. He doesn’t want to try and renegotiate with them, but says banks have been wary of offering a loan on the unconventional property.

The Sleepers also are not willing to accept donations.