When I arrive in London my journey can go a couple of different ways. If I'm feeling lazy I'll jump on the underground at London Bridge. It's a handful of stops on the Northern Line until Kings Cross, which is the nearest station to the Library.
I don't enjoy riding the Northern line at all, especially northbound and during the morning rush hour; It's hot, smelly and busy. I'm not particularly comfortable in large crowds.
When the weather is good I join the crowds and walk across London Bridge.
It takes me 20 minutes walking to cover 3 stops of the underground; it probably says a lot about the Northern line that I don't get to work any later!