Underground?

The ubiquitous London Underground train runs in the open in this part of London, and although one of the main highways into central London is nearby, the Underground still provides the quickest route.
Ever since I was a kid in short trousers, a trip to London was a treat because I would get to go on the Underground. In central London for the most part the tube network is entirely underground, and looking back, that probably was the principal draw. Trains that travelled Underground were unknown to me as a country lad, and getting what was then the rare opportunity to travel on them was an enormous treat.
Later on, whenever I was in London on business or for a recreational visit, I would always use the Underground to get from the train at Waterloo to whichever part of the capital I needed to be.
My visits tend to be much less these days, but if I needed to get about from one part of London to another, I would still choose this mode of getting there.