Russel Square is amongst many green spaces in London. It isn't large (takes less than 5 minutes to walk through it), but there are lots of areas you can sit down and relax. And unlike some countries, here you can sit on the grass.
It has a fountain and an Italian cafe, and there's a little coffee stall just by the North West entrance. You'll see lots of people working out in the morning, at lunch break there are lots of picnics happening, and people throwing frisbees around, and in the evenings loving couples - old and young - stroll their way around the perimeter of the park.
Great to take a break from the bustle of the city
Bloomsbury, London WC1B, UK