The underground safe house

More than an hour after leaving the coffee shop, Xia Pingan's figure suddenly emerged from the thick underground granite layer under the capital Circle of the country of fire like a ghost or a bubble. He looked at the medium-sized underground karst cave in front of him and finally smiled. He said to himself, " let's do it here, Yingluo.

The underground is not a piece of iron. Those who have experience in mine exploration, underground cave exploration, or underground tunnel excavation will know that the structure of the underground world we live in is very strange.

Besides subterranean rivers, there were also many naturally-formed caves or karst caves in the deep place.