Idea generation - London Underground.

Whilst in London, I normally find myself using the tubes a lot, which I personally think is a great idea; loads of people travelling and commuting  right beneath our feet. When sat or stood on the tube, a lot like the Train Journey theory, I find myself with a fair amount of spare time on my hands. This comes in useful when looking for inspiration or anything visual - it could be again on a person or in a paper ect. Also seeing all of the advertisements around the underground and on the platform always spark up some inspiration or idea.