On a hot day there is nothing better to do in London then go for a swim in the Heath ponds. You get completely transported you out of the city as Hampstead feels like being in the countryside except you're in central London?!
Hotter than hell, but always a good night had. It can be whatever you want it to be - restaurant, pub, or club, has good outside space and rentable rooms, and plays an interesting mix of music to an interesting mix of people. The building is actually kinda beautiful too.
Cosy little restaurant with a giant kitchen island unit in the centre which doubles as a display and seating area. Open for breakfast, lunch and dinner with a focus on fermenting.
The second coffee shop has to be Kaffeine. Having only recently come across this one, I was certainly impressed and they may even have the best coffee I've had, since a short stay in Portland, Oregon.