Despite the extreme poverty of most of these responses, I don't think this is an uninteresting question.

I tour. I go on long steady rides in training. In either case, I could be on the bike for six hours in a day. People have often asked me what I think about, whether I don't get bored, etc.

I thnk about lots of things. Where I'm going, where I'll stop, what I want for lunch, whom I'd like to be with me, all sorts. But most of the time I am not thinking, I am just being. I am aware of my surroundings, am in contact with my rhythms and the process of riding my bike, but I am not thinking, I just am. It's a Zen-like condition, these days they'd call it mindfulness. It's most restful.