On Tuesday, we went out to Greenwich to see the Naval Museum, and the Royal Observatory, which is at 0 longitude. The observatory is on top of a hill (where else would you put it?):

It's a long walk (and we managed to do it on one of the hottest days of the year!), but the view from the top is worth it.

Once at the top we did the classic:
Here we are standing in both hemispheres at the same time!