(Adult) Day out in London - any suggestions for a forriner?

[Fenouille]

I unexpectedly have a day to spend in London while I'm waiting for some paperwork to go through. I haven't been down to London for ages and don't have the faintest idea what I could do for the day. Does anyone have any suggestions other than BM/V&A/NPG? Indoors or outdoors, I'd just like to do something other than my normal routine (go to museum, wander, go shopping).

Thanks!

Cable car across the Thames on the Emirates Air Line cable car between North Greenwich and the Royal Docks? Only opened recently, so you will be among the earliest to experience it!
www.tfl.gov.uk/modalpages/23863.aspx

Ooh, sounds exciting :-) I was thinking of taking a boat to Greenwich so I guess that would fit in. I didn't even know that they were building a cable car in London