Out of the eleven Tube lines, seven of them are 'Deep Tube' whilst four of them are built just below the street at 'Cut and Cover' level. And if you know where to look, you can see the sections where they're not covered up and the underground lines can be seen down below!
A perfect lockdown activity as you don't even have to leave your home to do it, just use Google Streetview ...
3 май 2020