What is the one thing that most sums up London to you, or (because I think that might be too difficult!) the one thing that you would choose to do if you knew you could never go to London again and you just had time to do one more thing before you left.
For me, it would be a walk along the South Bank of the river, from Tower Bridge to the Eye. You see so many things, from famous sights to quiet back streets, from modern spaces to historic nooks and crannies. I love it.