Oh, the Hot Shot Furnace. Over the period of my starfort visits of the past few years, I have come in contact with several Hot Shot Furnaces, and have doted upon each and all. Fort Niagara's furnace, which was built in 1843, differs from all others in that it's built of the same stone as the fort's walls, as opposed to the standard red brick (although it's all brick inside, as brick can withstand mugh higher temperatures than stone)...it's also larger than any other I've seen, which is difficult to comprehend without a person or a donkey or something next to it for scale, but hopefully you'll take my semieducated word for it.

And speaking of semieducation, a Hot Shot Furnace was a common entity at American seacoast (and lakecoast) forts from the 1840's through the 1860's. It was intended to heat solid cannonballs to a red-hot state, at which point they would be carefully loaded and shot into the timbers of attacking wooden warships, with devastating results. Theoretically, at least. As far as I have found, there were zero confirmed cases of hot shot from any of these furnaces being flung at enemy ships...although it has been deemed "likely" that the Confederate garrison at Fort Macon probably at least tried to utilize this weapon in April of 1862 when under attack by the US Navy.