The fruit of empire, long after the empire has been eclipsed: you get to keep some of the things you acquired during your nation's reign of pre-eminence. In the Brits' case, one of those things is the Prime Meridian, which still runs through the middle of what was once the Thames-front palace and playground in Greenwich for Henry VIII, just downriver from The City.
The views from the hilltop site of the Greenwich Observatory are excellent - straight ahead you look over the former naval hospital (on the site of Henry's long-gone Tudor palace) towards the Docklands:
The City, Westminster, and all the other famous spots are in the distance to the left. That's the dome of St. Paul's you see on the horizon in the center-left of this shot: