I like to take photos of the underground, it’s full of people, of life, I find it interesting and it’s always a chalenge. But it’s also a bit difficult for different reasons: first, the light is not the perfect for a low ISO and second (and most important) in most cities it is forbidden to take pictures inside the underground (once someone told me in Madrid you can ask for a especial permission, but I never tried it)
Anyway, we’ll always have the exterior of the stations or take the pics without anyone noticing (but don’t tell anyone I say this)