Outside of the major players (Tate, V&A, RA) this is probably the best programmed gallery in London

A charming garden centre with cafe and restaurant, both located in beautiful greenhouses. Well worth a visit at any time of the year. 

One of London's best kept secrets, Spiritual Bar is a small and super welcoming live music bar on a side road near Chalk Farm station. Always somehow busy but not too packed, they play host to most of London's best emerging blues, rock and folk musicians, and owner Raf is the nicest dude you could meet. And makes a serious mojito

Some places are better to be left a secret. This one e.g.

6a converted a vacant mews warehouse in Bloomsbury into a set of spaces for the storage and display of art for a young art collector. The warehouse is situated in a cobbled mews, adjacent to artist studios, houses, a piano shop and a pub. Book a tour!