Not the most exciting place inside, but a lovely rooftop area which not all that many people seem to know about, 2 mins walk from Old St station. If it’s packed then The Red Lion is just up the road.
The Barbican has so much to offer! From beautiful architecture, to a conservatory, amazing art, films, music and performances. It is such an exciting and relaxing place to hang out. Even if you don't have a purpose for visiting the Barbican, it's good for just having a tea with a friend.
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!
If you want a peaceful day out of the busy city, Highgate doesn't really feel like London. The cemetery is interesting and peaceful, there's a tour of the old half which is definitely worth the money. Karl Marx, among others are buried there.
Although my skating days are now over, Stockwell Skatepark located just behind Brixton Academy is one of the reasons I moved to Brixton. It’s an excellent place, lumpy and hectic but totally friendly with decent Portuguese coffee and cakes just next door.
Ever since discovering this area around 6 years ago I still find it a nice area to go for a walk. Beginning at Paddington Basin with a mix of modern architecture which is fantastic to wonder around. Following the canal you go past a few restaurants and underneath a section of the A40 Westway before arriving at Little Venice and beyond.