The Longyou Caves. Discovered in 1992, no historical record or evidence of the work involved to excavate the almost million cubic meters of stone exists. The chiseling was done in such a way that it left a consistent pattern throughout the caves which some experts believe to be symbolic.There is also a rumor that seven of the caves have a distribution pattern that matches the seven stars of the Big Dipper.
A group of happy Finnish soldiers after defeating an encircled Soviet "motti." Probably summer 1941. Motti was a Finnish word that originally meant a measure of one cubic metre of firewood. The Finnish army used it to describe their encirclement tactics, first used in the Winter War. They divided the Red Army into "mottis", cutting them off from food and supplies and harassing them until they surrendered.
The Longyou Caves were only discovered late in the 20th century. At least 24 caves have been discovered so far. All of which were carved by hand. Although the overall excavation involved almost a million cubic metres of stone, there is no historical record of them or evidence of the work. Their origin is a complete mystery. At present there is no explanation for their existence. They represent one of the largest underground excavations of ancient times.:
On 21 October 1966, after several days of heavy rain, 40,000 cubic metres of debris from a colliery waste tip broke away and slid downhill towards the Welsh village of Aberfan. The catastrophic landslide hit the local junior school, killing 116 children and 28 adults. http://www.britishpathe.com/video/this-is-tragedy