Most don’t even notice the shabby metal hut, its cracked glass windows scrawled with graffiti, as they pass by the quiet cobbled square at the end of Franzeninkatu St, in a leafy district of east Helsinki.
And even fewer would imagine the vast world that lies behind its rusted doors.
We are led down four steep flights of concrete steps, covered by what seems like decades of dust, until, 25 metres below the surface, a long, sloping tunnel dug into solid rock stretches into the distance.
