I do remember that this is in the northern bastion, on the second tier. I was surprised to find such an oven (furnace?) up here, as it was of course swelteringly hot, and the temperature in the nearby Florida Keys is famous for only ranging from pleasantly warm all the way to moderately warmer...but a cheerful fire at night for a huddled, lonely garrison must have been quite a comfort. Even though the light emitted would have broadcast the fort's location for tens, perhaps hundreds, of miles to the north. But there was also Loggerhead Key Light blazing away all the time, too, so I guess the fort's location wasn't much of a secret.