Nearly every night since December, a strange booming sound has been startling residents of the northern Greek city of Thessaloniki.
Residents describe it as a deafening, even otherworldly, booming sound that can be heard in many neighborhoods across the city, but is most audible in the area where the roads Kifisias and Akropoleos meet.
Although many in Thessaloniki assume that the noise is coming from some sort of natural or even seismic phenomenon, Geology Professor Efthimios Lekkas stated on television news channel ANT1 that the noise is not likely to be natural of origin; rather, it may come from a human activity.