If you want a peaceful day out of the busy city, Highgate doesn't really feel like London. The cemetery is interesting and peaceful, there's a tour of the old half which is definitely worth the money. Karl Marx, among others are buried there.
Biblioteka is a library that collects and makes publicly available artists' books, photography books, zines, ephemera and publications on architecture and design.
They operate as an experimental library space exploring what a library could be.
After running 3 spaces in Kyiv, Ukraine their collection is now based in London, UK.