I'm currently building this 3d printed version of the Antikythera mechanism. It's not easy:

https://www.printables.com/model/284372-antikythera-mechanis...

It is insane how complicated this is, and this is a simplified version of the actual thing. This schematic of the proposed full mechanism (I think it's hypothesizing some of the missing parts) blows my mind: https://upload.wikimedia.org/wikipedia/commons/5/59/Antikyth...

If you have a 3d printer, I really am enjoying the project and recommend it.