When I used to live in London, cycling back from work was the highlight of my day. It kinda felt liberating (it was almost a 1-hour cycle). But then again, I used to sit at a desk all day, not run around saving lives and picking up drunks. I found the fitness bit a by-product. To me it help me clear my mind... come to think of it, I miss it. Also, London is a great place ot cycle.