I love that there's not only the internals of a standard three-hand, but the automatic mechanism as well. If you're going pure mechanical, an automatic is the best way. As long as you actually move during the day the watch generally stays wound up (though a twist when you put it on is a good measure). There's a ton of great watches out there powered only by walking around, and it's fascinating to look at what they can do with that.

The mechanics of a six-hand are similar, using the mechanism that is described here for the date indicator.

Another fun device, though more from an EE POV, are the solar+radio/GPS versions of the same. Automatics can hold power for a few days and need walking around to wind. Solar needs light (any light, though sunlight is always best) and hold power for over a month. Many higher-end models can self-set over radio time or GPS signals as well.

When the world goes tits-up someday, both classes of watches will suddenly become essential, and are already essential for people who spend a good amount of time "unreachable" for work or pleasure.