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.
The oldest public art gallery in London also is my local gallery in my neighbourhood. Opposite to the Dulwich Park where I walked with my puppy regularly. They have great collections of Dutch paintings as well. My husband found the original Dutch painting of the print at his home he was growing up with.
A very charming little shop with an amazing selection of spices, herbs and grains all stored in glass jars NO PLASTIC! :) You can also buy just the jars if you want to, they are really nice too. Finally a zero waste grocery store in the area. Thank you Charles!!