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.
I grew up around this area - it really is a gem of a place. The interior is so cool, with sort of organised clutter everywhere. They have a little garden and they serve food. Its not the best in the world, but the whole experience there is great.
Getting lost is an age old suggestion but a good one. Put away your cell phone or your A-Z and just wander around. I still do this regularly even though Ive lived here for nearly 10 years. London is a big city and it drip feeds you its secrets sometimes. You will come across things you wouldn't usually, in amongst the Starbucks and pret a mange there are some amazing sights. Just 'being' somewhere is a great experience and one no guide book can help you find.
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.