When I started learning CAD in 2012, what I really enjoyed was learning how to read the old blueprints. I am still amazed by how much detail and precision the engineers from the beginning to the middle of the twentieth century put into their drawings. I am nowhere near making those kinds of drawings, but I do enjoy making the drawings even more than making up the parts themselves. Here is a little drawing I did for some 1:16 scale parts for a model.