Kew Palace was initially bought by George III as a palace for the royal children. Many princes and princesses have been raised here! Later it was put into use as a summer residence for the British Royals.
The huge botanical gardens that lie around it occupy a whopping 121 hectares and have been on UNESCO's World Heritage List since 2003. The abundant flora and fauna will make you forget that you're in the London metropolis!
I can imagine in the summer would be even better.