Predicting the outcome of thoroughbred horse races. I am usually pretty good at it but not in yesterday's Belmont Stakes. My pick was Master of Hounds who finished 10th.
New technical certifications. The more difficult and challenging the better. The one I just finished three weeks ago was predicted to have a 50% failure rate among the advanced tecs who took the class. I made it.
I also love mechanical puzzles.
A good debate with someone who is well read and has an agile mind is very stimulating.
The most challenging thing that I ever attempted was taking spanish classes. After three years of twice a week classes, I had a pretty good vocabulary and could put sentences together, but I could never get to the point of being able to understand someone speaking spanish at a normal conversational speed. I finally gave up. It has been said that language is easy for a child to learn but adults have a lot of difficulty learning a new language.
I challenge myself by hiking up and down what look like impossible locations to get just the right photograph. It soothes my soul, keeps me in shape (or puts me back after this past winter), and concentration on my footing keeps me challenged!