Mahong and his team didn't follow the path the prisoners had taken to escape; instead, they circled around and accessed the first level through the normal maintenance passage. From the hole here, they descended underground and saw a wall that they had breached.
It was a red brick wall, not particularly secure, as the bricks were fragile and the mortar easily removed.
The hole in the wall wasn't large. Jimmy poked his head through and saw more pipes on the other side, including large ones. Judging from the temperature underground, one of them must be a steam pipe for heating. The others looked to be sewage and fresh water pipes. The breached sewage pipe Warden Valen spoke of was visible, with a gap large enough to allow a person to crawl through.
Because the sewage pipe was broken, the air in the space was foul, a stench only someone desperate to escape prison could tolerate. Just the smell, never mind crawling into the filth, would make most people retch.
