Hmm... just beneath the Arachnid membrane perhaps?
Image, feeling, word or phrase... but by whatever means that first spark of inspiration that is set for me is in a very precarious state of existence. I carry pen and paper rarely but yet when I do it seems that I never make that magic leap from what I see or feel to a describable event.
So, to answer the question; I write everywhere, only not with paper and pen or keyboard
( that usually comes only when I've roughed it out and I understand where I'm trying to go and what I really mean to convey for example "They Would Be Giants" was in my head for almost 4 years because I didn't truly understand what I was getting at.
) but instead with the minds-eye, it is the only thing that's ever worked for me, and in the long run much to my detriment I think.