The subway lines are the veins of a city. In Berlin they are used by tens of thousands a day, seven days a week, almost 24 hours a day. People drive to work, they want to meet friends or family, they are on the way to a restaurant or to a party. The metro is one of the most public spaces of a city, but also one of the most anonymous and lonesome. The man, who was just standing next to you, is just seconds later already forgotten.