I present to you "The Desmos of Aegelia" from the restricted collection at Miskatonic University. The artifact consists of two curiously writhing and fluted fish-like creatures made of silver and gold. A similar item is mentioned in the Cthäat Aquadingen, which describes the ritual joining of the two figures into an intertwined whole as part of a summoning ritual for the archaic fish-god Dagon.
It's first documented appearance in history is at the Greek seaport of Aegelia in the Second Century BCE, where it was reportedly used to bring forth a bounty of fish never before seen. While the fishermen of Aegelia prospered those from Marathon, just across the Bay of Styra, found their nets empty, leading to increasing strife between the two cities. The conflict came to a bloody head with the revelation that Aegelia's good fortune was the result of dark rites involving the sacrifice of children.
Of course that's all glurge, but it's the kind of set-up that can make something like this really shine as part of a tabletop or live action game. The "Desmos of Aegelia" is actually a cast metal puzzle from Hanayama called "Trout". They have an impressive line of small, beautifully designed mechanical puzzles that are ideal for re-purposing into artifacts and magic items.
Puzzles like this are a hugely overlooked game resource. What makes them particularly neat is their natural immersiveness. Fantasy is filled with characters reuniting the pieces of ancient artifacts for both good and ill, to the point that it's become a handy series of tropes (Dismantled MacGuffin, Set Bonus, Two Halves Make a Plot). At the most basic level, each piece of the puzzle can serve as a plot token advancing the story. Then the players have to physically reassemble the completed item. While that can be a bit meta, relying on player skill instead of character skill, I've never run across a gamer that wouldn't find the process engaging.
One thing to be wary of is difficulty. "Trout" is a Level 1 puzzle that's relatively easy for even a beginner to figure out. The Hanayama scale goes up to 6. At that point you're dealing with fiendishly complex puzzles that can stump even the most gifted. To alleviate some of the potential frustration you may want to convert the puzzle's solution into an in-game document or hint.
Here are a few specific puzzles for prop use. They're all around $10 in price, which is a bargain for anything precision cast in metal.
"Flag" is another easy puzzle that has the advantage of looking like a key or part of a larger mechanism. You could create a matching "keyhole" by impressing the flanged end into polymer clay or epoxy putty.
"Equa" is a tough Level 5. On the bright side, its spherical, tri-lateral symmetry really does look like an alien artifact.
"H and H" is a beautifully polished two-piece puzzle of moderate difficulty. Perfect for the "Two Halves Make a Plot" trope mentioned above.