A Strange Structure

On my evening walks with my dogs for years I have noticed a strange old brick structure in Cottagewood. Shaped like a cylinder, I wondered what it was. Having lived in St. Paul’s Highland Park I assumed it was a water tower like the Highland Water Tower (the highest point in the Twin Cities). Upon my reading, my assumption proved correct.
The origin of the tower is unknown, but most think it was a private water sourse for the Keewaydin Hotel built in 1892-1924, when the hotel burned down.

The tower was modified in 1911 by Arthur Dyer, a local shipbuilder of some reputation. It provided water to Cottagewood untill 1941 when it was abandoned after attempts to sell it failed. Still, there it stands... I wonder what is inside?