[Gargoyle]

One fun (if not particularly practical) path is to learn the Atari 2600 video game platform.

Documentation is readily available, along with source code to a number of classic games. There are several emulators and even a small community of people turning out new games for the platform.

The 2600 was/is quirky, and of course it's ancient history, but it does provide a path to learning some basics that still apply today. Most importantly, it's fun.

Start here as a resource - http://www.atariage.com/2600/programming/