Not many artifacts from 500 years ago strike this kind of balance between "astounding" and "skin-crawlingly creepy", but this windup toy mechanical monk certainly claims the title. The thing works perfectly; on winding, it marches around in a square moving its arms and head, mouthing (presumably) Latin chants. Here's a video of the device in action:
It's just one example of automatons, a lost art of entirely clockwork mechanical toys and figures. In this day and age, the sum total of animated figures most people may encounter in a lifetime is at a theme park. We know some of the arts from this era, such as cuckoo clocks and coin-operated fortune tellers, but few appreciate just how hard Renaissance people worked to try to make convincing androids using only gears, chains, and springs.
You'll find many more examples at the UK site House of Automata. Here's a few more fascinating artifacts from this lost, magical era:
And there were quite a variety of clever mechanisms deployed for these. For instance, why wind a toy when you can power it entirely by dumping in a bucket of sand?
And here's a Chinese magician set from 1920 - doing an actual magic trick!