I like this video on an 11 day level design
This video is really nice. This gives me another idea. I usually focus on programming, game component design, and visualizing the games during the game a week, but this makes my skills kind of one-dimensional. Instead it would be interesting to focus on a completely different sub-craft of game development, like level design or asset creation (art, music, other?) for a week, and then do a write-up on what's learned as well as the results (no actual game, just whatever content is iterated on or created). This will help to understand the other sub-crafts of game development deeper for when I work in teams with artists/musicians, etc. It will also be a good way to become familiar with those pipelines and tools in those fields.