Level 4 takes Carl and Donut to the Iron Tangle, a mess of subways and stations that push the endurance of all of the crawlers.
By chance, the Dungeon Anarchist‘s Cookbook, a compilation of experiences and tips collected by crawlers who had the book in past dungeons, finds it way to Carl. He reads it in secret and uses what he can to help get his allies through to the next level. He also starts plotting to bring the whole system down.