An underground city is a series of linked subterranean spaces that may provide a defensive refuge; a place for living; a transit system; storage cellars; cisterns drainage channels; or several of these. Narrow roads of the inside the cave. It is the largest excavated. The Stone Age was a broad prehistoric period during which stone was widely used to make implements with an edge, a point, or a percussion surface. Neolithic house, archaeological features archaeology. Historic rock cavities cavern grotto ancient historical tunnels tunnel floor rocky deepened deep settlement caves passage wall walls volcanic granite ventilation corridors corridor settlements old ruins ruin antiquity primitive gate road mesolithic diachronic holocene era historied palaeolithic paleolithic UHD 4K 3840X2160.