Short backstory - a lump of bronze was found in a shipwreck 116 years ago, near the Greek island Antikythera. Once properly analysed in the later 20th century, it completely changed historians' understanding of how far mathematically and mechanically advanced the ancient Greeks were. However, in 2006 the artifacts were subjected to CT scanning, and vast amount they learned about the device basically blew their minds.
This thing has been around a while - perhaps you've already heard of it. But an Aussie has decided to document his reproduction build, and his work is at once fascinating, elegant and utterly captivating.
So far he looks to be 80% done. Episode 1 is below, and there are 6 more at varying lengths. His YouTube channel, Clickspring, also documents him making various tools for the build, along with other projects. It's simply mind blowing.
https://en.wikipedia.org/wiki/Antikythera_mechanism