Those scratches look like heavy machinery getting dragged in and out of the tunnel entrance. Think industrial HVAC packed in a metal crate or metal framed pallets used by military and container vessels. My guess is the wide entrance is Air filtration for intake and the small one is the outtake. Hence no heavy duty access ramp on the smaller opening. Most dense rock gives off radiation and good air circulation is a must. That and human viscera tends to get rank while the stench will become embedded without said air pumps.