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.
This is the place where ghost pirates roam in times forgotten. Where great poems were once written. Everything has happened here. A few abandoned boats and much stillness. And an island in the middle. Most curious. Not much choice but to explore as far as your nerves will take you. Watch out for Zorro the dog.
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?!