For a brief period of time, approximately between 1500 and 1530, a series of miniscule boxwood carvings were produced by an unknown artist in Flanders or the Netherlands. The carvings were made as religious items, and they are tiny and complex enough to have been baffling the experts to this very day.
Each boxwood carving piece is estimated to have been 4 to 5 years in the making, and part of the mystery is that they all seem to have been created by the same person. So how did (s)he manage to produce them all in the short time span of 30 years? Part of the explanation may be that they were made in a series of different workshops, run by skilled apprentices. But that does not explain how all the miniscule details, almost invisible to the naked eye, were managed.
Sure, eyeglasses were invented in the 13th century, but even with modern-day technology it is hard to discern all the details. I seem to recall having read somewhere that children may have been involved since, usually, they have better eyesight and smaller hands. But I doubt somehow that they had the insanely impressive carving skills required.