Wulf makes a very valid point which I should have added to my Walk It! post.
Another great advantage of walking around London is that you get to see things that escape your attention when you are rushing past in cars and buses (rushing being a relative term in London traffic) or passing underneath them on the tube.
London has wonderful architecture and lots of hidden visual gems, but we so often miss them.
One of the things that has most made me appreciate Forest Hill, and London architecture and design in general, is a group of Londoners that challenge each other to identify photos that can be taken anywhere within London. Check out the "Guess Where London" group on Flickr.com but I warn you, it can be addictive!!
Since I joined this group I look around, and UP so much more than I used to and it is amazing what you see, particularly around areas you thought you knew.
So get walking, and get snapping too!