Matt Brown in his excellent blog series The Scientific Tourist in London provides an fascinating account of a pedestrian crossing in the north western corner of Russel Square. It was here that Leo Szilard is said to have conceived the nuclear chain reaction in 1933. Unfortunately, there is no plaque or stone to mark his discovery so after you've crossed the street this plan already comes to an end. You can still have a picnic in Russell Square or visit the British Museum in the area.