My grandmother used to say that in order to remember a thought, she had to go back to the place where that thought was originally conceived because place triggers her memory.
I find that there are certain thoughts I have in particular places. When I'm on the mat at the gym doing my stretches I've noticed that a certain thing often comes to mind. Because I'm not on the mat at the gym right now - I can't remember what it is! (And, no, the thought has nothing to do with exercise.)
source: Butterfly Boy: memories of a Chicano mariposa by Rigoberto Gonzalez