I love to have Piccadilly Circus as a meeting point, when I am in London.
I just seat on the steps, watch all the movement of the circus: so many different people from so many different cultures walking around, groups of friends meeting there, hanging out. Waiting to meet other people and go somewhere else. And the light around it. Buses never stop passing by, people walking through it at any hour.
London is a city full of inputs; I’d need to take a break after some days, if I stayed longer than 4-5 days…!