Hidden away in a residential neighbourhood is one of Afghanistan's new "secret" schools - a small but powerful act of defiance against the Taliban. Around a dozen teenage girls are attending a maths class. "We know about the threats and we worry about them," the sole teacher tells us, but she adds, girls' education is worth "any risk". In all but a handful of provinces in the country, girls' secondary schools have been ordered to remain closed by the Taliban. At the school we visit, they've done an impressive job trying to replicate a real classroom, with rows of neat blue and white desks.