Anyone strolling through the World Heritage city of Baden-Baden these days will inevitably come across an impressive structure.
It stretches for kilometers through the streets, a thick blue tube supported by blue steel girders high bove the road.

What is it?
Is it the development of new thermal water resources?
A test track for transmitting massive amounts of digital data?
An art installation?

No – none of the above!

The sewer system is being renovated, and a bypass had to be created for rainwater and a small stream that flows underground through the valley.