It does what it says on the tin. You turn up with a book you no longer want and add it to the collection and then take a book from the shelf that you'd like to read. Sounds a nice idea and yes, you say, there are lots of places that do that. But not all of them provide you with some comfy sofas and vintage chairs and a place to relax and read your new book.
OK - now we're talking, but it gets even better than that. If you really want some peace and quiet, they even have their very own private reading rooms, where you can lock the door and completely immerse yourself in the joy of reading and away from the crowds outside.
See I told you it was good. I'm sure they wouldn't be adverse to you doing some writing while you were there too.
And when you're done with reading and you need sustenance, you can wander up the street to The Timber Yard for coffee, tea and all sorts of yummy loveliness.
Here's what we had for breakfast - Porridge with Bananas and honey and coffee of course!
I'm definitely putting Seven Dials on my 'return to when in London next time' list.
I think it could be my new best favourite place.