Curt and Deborah Sleeper want to sell their underground house.
The home is built inside a cave in suburban St. Louis.
Of course, an underwater home refers to house that's now worth less than its outstanding mortgage.
The Sleepers have put their three-bedroom cave home up for auction on eBay.
Bidding starts at $300,000.
The Sleepers say they have a big balloon payment due and they haven't been able to arrange new financing.
They add they might not sell if they're able to get a new loan for their cave.
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