I also got bored at regular gyms, and realized that combat-oriented martial arts may be the ultimate problem-solving challenges. You have to muster all your intellectual and physical capabilities "against" an intelligent opponent who acts/reacts "in realtime", but also is prepared to it (the boulders layout is carefully crafted beforehand, but it doesn't react!). Jiu-jitsu may be one of the most adequate because it seems not as dangerous as striking arts (albeit by becoming competitive one may gain serious back-related aches or even injuries).