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!
The Royal Park offers great views of London and the city; As well as housing the Royal Observatory which includes a museum of astronomical and navigational tools, part of the National Maritime Museum.
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.