> with the rails literally 20ft below the street. Some nice pictures about this: https://de.wikipedia.org/wiki/Unterpflasterbahn https://de.wikipedia.org/wiki/

> with the rails literally 20ft below the street. Some nice pictures about this: https://de.wikipedia.org/wiki/Unterpflasterbahn https://de.wikipedia.org/wiki/Unterpflasterbahn Note that not all U trains in Berlin are like that, some are deeper (with a mezzazine) and some are partly on elevated tracks or outside the city they go overground just like normal trains.