@af @th Unfortunately concrete is one of biggest CO2 polluters in our fight against climate change, more polluting than all transport together. The industry doesn't want to change while there are good alternatives. Hence it impairs seeing the beauty any longer.

@th we have something similar here, but at least for one of the two tubes, most people will stand in the rain waiting for the train: https://en.wikipedia.org/wiki/Elbbr%C3%BCcken_station