Granted, we are talking about "thinkers" here. We can think sitting on the toilet or taking a shower, and maybe even better than staring at a book.
Walking to get your juices flowing surrounded by clean air and a soothing environment would make any hiking trail a great office for any scientist or philosopher.
"It's not that I'm so smart, it's just that I stay with problems longer. "
― Albert Einstein
"Richard Feynman was fond of giving the following advice on how to be a genius. You have to keep a dozen of your favorite problems constantly present in your mind, although by and large they will lay in a dormant state. Every time you hear or read a new trick or a new result, test it against each of your twelve problems to see whether it helps. Every once in a while there will be a hit, and people will say, 'How did he do it? He must be a genius!"
- Gian-Carlo Rota, Indiscrete Thoughts