I'd personally be most interested in a language acquisition trial, specifically some kind of intensive course. It might be possible to find an out-of-the-box program that would have the potential for surprising results. For example there's a program called 'Remembering the Kanji' that's interesting to me because it's both incredibly effective and never taught in school. I started last week doing 50 a day, and have learned stroke order and keyword association for 450 kanji with almost perfect recall. In the past year of traditional study I learned maybe 200.
Unfortunately this obviously requires intrinsic interest in a language or culture. Maybe with a little research you could find other indirect benefits. A quick Google search gave me
this article. It seems it applies best to those who learn young, but that's the point of a 30 day trial
If nothing else you might pick up some new learning and memory tricks.
Something more appropriate to you personally may be charity work though. Try joining some organized charity work and see how it affects your perceptions and self awareness. Some areas would have the potential to be both confronting and rewarding, which would be interesting.