Not the most exciting place inside, but a lovely rooftop area which not all that many people seem to know about, 2 mins walk from Old St station. If it’s packed then The Red Lion is just up the road.
SOAS university has a small gallery space dedicated to exhibitions about Asia, Africa and the Middle East. There's a small but beautiful Japanese zen garden on the rooftop (currently closed for refurbishment)
Always interesting exhibitions and a nice little shop selling magazines, prints and books.. Small and simple gallery, surrounded by Hyde Park's beautiful elegant landscape.