The London plane is a hybrid that does well in city soil and tolerates pollution. It was planted across central London in the early nineteenth century, and the specimens in the Bloomsbury garden squares are among the oldest in Britain. The trunks are massive, the canopy is high and wide, and the leaves are large enough that even on a still July afternoon the squares are several degrees cooler than the streets one block out.
Bloomsbury is a six-square neighborhood — Russell, Bloomsbury, Tavistock, Gordon, Woburn, and Brunswick — laid out on a roughly continuous grid. The walks below string the squares together. You are never more than a block from canopy. The picks are graded for the increasingly hot Julys London now gets; in a cool year these are simply nice walks and the shade math is overdetermined.
A practical note: most of the squares are private gardens in the technical sense, but most are open to the public during daylight hours. Russell and Bloomsbury are always open. Tavistock is open weekdays. The Stay Cool router will quietly bypass any square that is locked when you arrive.