Solo tasks that require much focus and time

Through some personal conclusions and readings within history of all kinds, one can see how tasks back then had a person focus completely on it for a very long time until it was completed such as in the distant past of someone trying to domesticate their house or a single student attempting to solve on math problem or with the "adaptation" of doing a painting, etc.

List some tasks that either you have seen, heard of before or that even you do that requires only yourself to do but that also takes a long time.

Masturbation.

...sorry, couldn't resist.

I've seen the same response elsewhere, even today. Such deja-vu.