Black and white film processing. It used to be taught in schools. Many schools still have their darkrooms and no longer use them. It is a practical application of physics, chemistry, and art.
As a kid (11 or 12) I made an enlarger out of an old discarded slide projector, a dimmer switch and a scrap wood frame. I managed to scrounge enough money to buy supplies to make a few prints-- it worked pretty good. But, supply costs were out of reach, so those first prints were all it ever made.