The Greenwich Observatory with its green laser beam can transfigure any night sky. If you decide to cross the Thames via the foot tunnel, make sure you look out for the green ray. You can be on one side of the meridian in a minute, and cross to the other side on the next, without even realising it.
It is one of the most important business centres in London. Crowded of suits at daytime, perfectly deserted at night. It is so striking relaxing to walk in there enjoying the silence and the lights! It makes you feel pleasantly far from reality.