I've written about Columbia Road Flower Market before- and this year I was more than happy to return!
The street absolutely fills with tourists and shoppers alike. The market only runs on Sundays until 3PM - so I would recommend getting there early to avoid being choked by the crowds.
But despite the crowds, it's always worth a browse just to see the proliferation of blooms just waiting to be wrapped in brown paper for the tube journey home.
Now take the colours you've just seen, and add the smell of fresh cut flowers and herbs, combined with the sound of street hawkers charming the crowd into buying. I think we have a winner.