The underground station Bonner Wall in Cologne, seen from the southern end
on 13 December 2015, the day it was taken into service. While this station and
the southern tunnel branching towards Marktstraße  and
Schönhauser Straße (not in the picture) were built by the
cut-and-cover method, most of the new line through the city was drilled by
tunnel boring machines. The beginning of the two separate tubes (one for each
track) can be seen in the background. There is an intermediate level at each end
of the station, separated from the big hall by glass walls.
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Digital photo by Christoph Schmitz
(<a href="mailto:christoph.schmitz@rwth-aachen.de">christoph.schmitz@rwth-aachen.de</a>)