This post by Nancy Duarte about how taking long walks inspires her, resonated with me. She describes the experience of shutting down your brain to help you focus and be more creative. Almost all pleasures in life are someway or another about cutting out noise, worries, and random thoughts out of our mind.
Ancient oriental wisdom encourages us to focus deeper on the natural experiences of enjoying what we eat, making love, meditation. Artists try to create a disconnected world through a good story or beautiful craft. More brutal, unhealthy, and/or illegal ways to reach that stage of disconnection are alcohol and other banned substances. Mass media tries to achieve that same escapism through retail therapy, (loud) music, or bone-shaking visual effects in movies. Endurance sports fanatics can even get hooked to to beta endorphins that are released as the result of heavy exercise.
Nancy choses hiking, I use mountain biking as a way to shut down the brain. It is the perfect combination of being outdoors, doing a physical workout, but also requiring your brain to focus heavily on obstacles on the trail ahead of you and being aware of the balance and flow of your body at all times. There is literally no time to think of anything else.