During my outings I'm always on the lookout for an old clock, particularly old alarm clocks and mantle clocks.
Why clocks? First, the mechanical nature of old clocks intrigues me -- I mean they have gears, and sprockets, and springs, and levers -- all sorts of neat stuff that, when working as designed, actually captures the passage of time! Second, except for rare expensive clocks, when an old clock quits working, most people assume it is done for.
What I have learned over the years is an old clock can generally be fixed -- often very easily. And, if it can't be fixed, AND it is of a style that is interesting, it can always be converted to a quartz movement, but I only do that as a last resort.
This Instructable won't make you an expert in clock repair, nor will it cover the details of clock repair, but I will try to go over what I generally find wrong with these old clocks and how I get them running.