In Athens and the general Attica region, there are several underground shelters that the majority of the population are completely unaware of.
The underground air-raid shelters had been built before the World War II era and have never been used as Athens was not bombarded during World War II.
There are no official records of the underground shelters, however. Other than the Greek army and the Civil Protection, few have knowledge of their existence and exact location.
History of air-raid underground shelters in Greece
The Ioannis Metaxas regime, which came to power with the August 4, 1936 coup, considered that an impending armed conflict in Europe was very likely to take place.
Moreover, Metaxas knew that war on the air was going to dominate in the next war, and, consequently, bombardments in urban areas were more than probable.