the Antikythera mechanism is an ancient greek device recovered from a shipwreck near the island of Antikythera in 1901, and for decades nobody fully understood what it actually was, just a heavily corroded lump of bronze gears. modern imaging techniques, especially x-ray and CT scanning done in the 2000s, revealed it was an incredibly sophisticated analog calculator used to predict astronomical positions and eclipses, essentially a mechanical computer over 2000 years old, way more advanced than anything else known from that era. it's now on permanent display at the National Archaeological Museum in Athens, and researchers are still studying it to fully understand every function it had.
calling it a mechanical computer from over 2000 years ago still doesn't fully compute for me, the complexity is insane for the era
the fact that it took modern CT scanning to even figure out what it was says a lot about how far ahead of its time it must have been