Of ghost stations and other subterranean public spaces.

On the day of our visit to where the Wall was, and isn't, Diana and I discussed this very phenomenon of ghost stations. I remember them from 1989.

This exhibition, on display at the historical site of the Nordbahnhof S-Bahn station, recalls a special chapter in Berlin’s history of division: the closed-down and heavily guarded train stations of the U-Bahn and S-Bahn lines in East Berlin. The stations were only used by trains coming from the West. The exhibition describes underground escape attempts and the border fortifications built to prevent them.

The exhibition in the Nordbahnhof station shows the absurdity of the division on the basis of three U-Bahn and S-Bahn lines that crossed through East Berlin while traveling from one end of West Berlin to the other. Between 1961 and 1989 these lines had a special status within the city’s public transportation system that was otherwise divided. The trains of these lines (today’s subway lines U6 and U8 and the north-south rail of the S-Bahn) no longer stopped at the deserted train stations in East Berlin and could not be used from there. For West Berliner’s, the daily passage beneath East Berlin continued to be a strange experience. The closed-down stations came to be known as “ghost stations” in West Berlin.

But who knew that Cincinnati has a 90-year-old unused subway?

The weird afterlife of the world's subterranean 'ghost stations', by Drew Reed (Guardian)

In 1920, construction began on what was to become an important new transportation system for Cincinnati, Ohio. Local voters had given near-unanimous support to a $6m (£3.7m) municipal bond, and despite wartime restrictions and shortages, the project began. Little did the city’s officials know that the system they were building would never carry a single passenger.

Five years later, the money had run out, the federal government refused to help and construction was halted. Today, there is an entire six-mile subway system abandoned underneath the Cincinnati streets.

Though Cincinnati’s empty subway is an extreme example, it’s part of a global phenomenon that’s actually quite common. Underground travel has become a familiar routine for millions of urban dwellers, but most commuters are unaware that lurking on the other side of the walls are the remains of abandoned stations, slowly deteriorating. Known as “ghost stations”, they are silent but powerful reminders of forgotten history.