This is an Easter Egg in the game.
The skeleton, which is hanging upside-down from the icy cave's ceiling also has a glowing, enchanted sword on the ground nearby. This is a reference to Star Wars, where Luke Skywalker set off a trap in a cave in Hoth causing him to drop his lightsaber and hang from the cave ceiling.
the hanging gardens are a giant pillar of stone, hanging from the ceiling of a giant cave. The whereabouts of this cave are unknown.
its in one of the guards inventory
cave
A skeleton of a prehistoric man was found at the Old Mobile Site in Alabama near the city of Mobile. This archaeological site has yielded important information about the Native American populations that inhabited the region thousands of years ago.
A stalactite.
Hanging down from the cave roof are stalactites.
Near the skeleton of the dinasour above the cave men.
Well I know Septimus is in a little cave/hut thing north of College of Winterhold.
it means that skeletons have died or there is chests underneath
Stalactites hang down from the ceilings of caves.
A cave deposit formed by precipitation of calcium carbonate from groundwater entering an underground cavern which forms a hanging feature from the ceiling or wall of the cave.
The Skeleton Key is actually not an item as you would expect but a button of sorts. In the Sealed Cave of Final Fantasy III there's a dead end with skulls. One of these skulls is the actual key you need to interact with to proceed.