I was given a big box of leftover embroidery thread and I have been using it learning to make temari balls. They are made by wrapping yarn and then thinner and thinner thread around a core until it forms a ball, dividing the ball and marking it with thread and finally stitching geometric designs over the markings. I am still very much a beginner but these are really fun to make.
I would say the initial wrapping usually takes me an evening, so 2-3 hours. Then the marking may take 1-2 hours depending on the type. And the embroidery can vary a lot depending on the design. It can take 2 hours, it can take 10.
But the process is very satisfying. You can see your progress and the geometry of it all is really fun to observe and build upon.