If you fancy a peaceful afternoon then head to Holland Park where you can sit, relax and enjoy the Kyoto gardens. It's only a short walk from the Holland Park tube station, you could definitely spend a sunny afternoon here!Little Venice | Tube Station: Warwick Avenue
Holland Park is a park again near where I used to stay. A smaller cousin to Hyde Park, its often lost in the shadow of the Big Brother. but its a nice place, have been there at least 10 times. There is the usual cafe and games to keep you busy but as I said, Hyde Park is definitely better:).
For some breathing space head to the ever-so-chic Holland Park, which hold a Japanese garden, an opera house and even peacocks.