Postcard from... Cologne

The soaring twin spires of Cologne's mighty cathedral stood tall throughout the Second World War although the ancient building, which began life in 1248, was hit no less than 70 times during allied bombing raids on the city. But now the UNESCO World Heritage site faces a different and more insidious threat – namely the city's recently opened underground metro line. Cologne's Catholic provost has raised the alarm by complaining that the vibrations caused by the trains are prompting the cathedral to wobble.

He has warned that they may cause long-term damage to the structure. The tourists who each year make the cathedral Germany's most visited attraction, have also noticed vibrations inside the building and on the steps outside. A deeply concerned Cologne city council has reacted by imposing a 20 kmh speed limit on trains passing under the cathedral and has asked for a full investigation. However the council is reported to have failed to notify UNESCO about the threat.

Cologne's new north-south metro line has already caused a series of major and sometimes tragic headaches. In 2004, construction work caused the tower of St John the Baptist church to start leaning over. In March 2009, work on a tunnel caused the city's historical archive to collapse. Two people were killed. The metro is scheduled for completion in 2019. In the meantime church officials are insisting that the cathedral wobble poses no immediate threat. They point out that it not only survived the Second World War, but also last year's Fukushima earthquake and tsunami, which caused the cathedral to rise and fall by up to a centimetre several times.