From the O2, walk on spooky, atmospheric Thames riverside, see the meridian laser beam, Maritime Greenwich, a city farm, waterside docklands walkways and skyscraper views at night, to Canary Wharf. Bring a torch (most is lit). If you want to learn of the social and maritime history of this diverse area before walking it, spend the same afternoon at the Museum of London Docklands (free entry, next to Wetherspoons). Meet up at the Museum (cafe) at 1pm, leaving at 5pm for North Greenwich (one stop on Jubilee Line)