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.
Hidden away in the backstreets of Finsbury Park, I used to share a house opposite this pub, where it assumed the role as our second living room. A real north London gem, I still go there these days for the tree-house-like, leafy terraced beer garden, which is perfect for summer evenings.
An unassuming glass door on an otherwise plain facade hides a cavernous space, with high ceilings and huge sliding partitioned walls producing excellent exhibitions in a space you'll want to go back to.