Although it might seem like a bargain, the drawback is there is no way to get into the 12sq m first-floor space.
However, the room, wedged between two properties and suspended over an alleyway in Wisbech, Cambridgeshire, appealed to one bidder whose hand shot up when the £1 price tag was announced.
The guide price of £100+ was dropped to £1 at the last minute.
The unusual property is in a terrace of old buildings, believed to have been built as granaries or shops in the 16th Century on Nene Quay.
It is bricked up from both sides and even the auctioneer had not been in to see it.
Fenland District Council, which has owned it since 1966, put it up for sale alongside other "surplus properties" with Norwich-based auctioneers William H Brown.
There is no record of anyone ever having used the room and the contents and condition remain a mystery.
When it first went on their books, auctions partner Victoria Reek described it as "certainly one of the weirdest ones we've had at auction" and admitted it was "probably just full of cobwebs".
She said the vendor instructed the auctioneer to remove the £100 guide price just before the auction opened.
"So we told bidders the first one to offer £1 could have it - one gentleman put up his hand and it was gone - all done and dusted," she said.
It is not yet known who bought the inaccessible room.