Warm summer nights should be spent in the high grass in Hampstead Heath above the ponds. For midsummer bring herring, snaps and songs and stay until sunrise!
East london spot with a bit of everything, food during the day and cocktails, music and cinema during the night. Few nice places around like E5 bakery, Netil 360 rooftop, and Mare Street Market
The Premises is cozy café attached to a recording studio in Hackney (frequented by Nina Simone, Al Green and Jarvis Cocker over the years.) Lovely people serve up tasty breakfasts and Turkish food in the evening.
Free natural ponds, open all year round (check online for varying opening hours according to seasons). Get an absolute get away feeling right in the heart of London, a treat if you enjoy swimming with ducks. Amazing park to enjoy a few games of cards and a walk around afterward too...