DON'T OPEN IT! It is actually a medieval fruitcake container, probably still containing fruitcake from the 14th century.... it probably should be registered as a biological weapon with The Hague!
Looks like a bucket to hold a heated cannonball on a wooden sailing ship of yore.... No fires allowed anywhere except the kitchen. So, to heat a cabin, a hot cannonball was suspended in a metal bucket, radiating heat.