Surgery inside the Underground Tunnel

Every step of the underground tunnel was three meters long, one meter wide, and half a meter tall. Each step was a giant stone slab; it was the same material that built the high walls. The stone surface was covered with a strange dark red pattern. It looked like blood capillaries. The steps led underground. The walls on the side were of the same stone material as the ceiling above them. There was no trace of dirt or sign of any living plants like lichen. It was as if the underground tunnel was carved out from the stone layer. Each stone was in itself a complete entity, but if that was the case, how could they keep the surface of the stone so even? It was as if the stone steps were made by nature.