The latest bid for the Round Island Passage Lighthouse was $20,000, as of Tuesday. The sale began Monday with an opening bid of $10,000.
The Detroit Free Press reports the online auction is open to nonprofits only who must register to bid.
The building with a 71-foot tower is on state-owned Great Lakes Public Trust bottomlands, which isn't being sold.
The Round Island Passage Lighthouse opened in 1948 to mark a passage between Mackinac and Round islands in Lake Huron.
Auction site: http://1.usa.gov/1rSOu5x