Up to the age of thirty, I used to get on the bus, go to the terminal point, and come back. To clear my thoughts. I've tried this both in India and while I was a student in the US. Found it immensely beneficial. Unfortunately I live in a city which lacks public transport, so can't do it any longer.
Funny, I've found that the best place for me to concentrate is on a bus or train, provided there's not too much noise around. During one hour journey I can usually accomplish more work than 3-4 h in home/office.