Welcome from the San Francisco, USA area.
Went to London back in 2005 and it may be my favorite place I've visited. Where I live, everything is less than a hundred years old, so I must have looked like a real rube walking around just marveling at everything around me. And it has so many aspects of a great place for travellers: an easy and comprehensive transit system, lots of free attractions, friendly people, etc. Just loved it.