The bronze Roman dodecahedron has famously puzzled everyone as to it’s purpose - even historical experts.
What other items do we have from the past that we can’t confidently identify the utility of and that it’s purpose has continued to confound us?
The “Baghdad Battery”.
Any time you take two dissimilar metals and immerse them in anything acidic it just naturally makes an electrical cell, so the fact that it does actually make a functional “battery” is probably just coincidence. Plus, there are no electrical connections anywhere on it.
On the other hand, no one has yet to come up with a convincing explanation of what it was actually used for.
It’s neat to see innovation like that even if it didn’t function in a way we can confirm. I wonder what it was like for the inventors back then. Maybe they could get grants or funding in those eras.
That’s cool and equally baffling. From the linked article:
" The artifact disappeared in 2003 during the US-led invasion of Iraq"
Yikes! 
Diquís Spheres:
Maybe it was a party trick. As they’d get drunk they’d dare each other to touch the zappy thing.
There are also the mysterious carved stone balls (band name!) of Scotland:
Who the fuck builds a stone henge?
It’s killing me that no one knows
Why it was built 5,000 years ago
Eddie Izzard may have an idea about that (comedy):
That would have been a bitch to roll a15+ ton rock around to carve the other sides.
The Iron Pillar of Delhi is supposed to be fairly mysterious. The claim is that it is 1500 years old, but shows little or no signs of corrosion. It is 99.72% composed of iron. It was made “400 years before there was a foundry large enough to cast it”. I can’t say how much of the claims are accurate and how much are baloney.
The Nanjing Belt is another “mysterious” artifact. The mystery is that the segments have a high aluminum content in the alloy, but they allegedly date to the 3rd century, when the ability to smelt or extract aluminum was not developed until the 19th century.
Wikipedia has a list of Ooparts (Out of place artifacts) which are items that don’t seem to make sense for the context in which they were found.
The Phaistos Disc.
It appears to be a circular tablet with some kind of script or message pressed into it, but nobody has deciphered it, or even properly identified the writing system. despite many attempts and some claims of breakthrough.
In ancient times,
Hundreds of years before the dawn of history
Lived a strange race of people, the Druids
No one knows who they were or what they were doing
But their legacy remains
Hewn into the living rock, of Stonehenge
Fascinating read. Presumably, since that ‘font’ was pressed into wet clay, there are other examples that are either undiscovered or have been destroyed.
ETA: Maybe there was an equivalent of book burning by an incoming ruler?
The *Bible rock on the other side of my pond.
Not a particularly rocky area. Just a funny shape with one squared off corner. That looks cut.
The kids have speculated for years. Gold nuggets underneath. An alien vessel that hit so hard it partially buried itself. A pyramid someone forgot to finish.
I’m waiting on the big wigs from reality show fame to come turn this place into another Oak Island. Any day now.
Yep, I’ll be raking in the bucks. For sure.
(* We call it Bible rock because we don’t have a family Bible and all the kids have put their names and birthdays on it. And many other folks)
Voynich Manuscript
We had a wood henge here once but it rotted.
Yeah, what’s really tantalising about it is - if that really is a script, this was made using basically movable type, invented at least a couple of thousand years earlier than the earliest other example of movable type in China in 1040 or so. The Minoan version just didn’t seem to catch on though.