the dungeon anarchist's cookbook - Matt Dinniman

Forward: the fourth floor is a confusing maze.  So if you don't understand stuff, don't worry about it.  There will be a map at the end that explains it all.

Ch 1

We really get off to a running start here.  Our 3 member band is on a moving subway car.  They are on car 20.  The newest member of or team has advanced mapping skills and can see that things don't get interesting until car 15, which is marked with a big question mark.  They dont do anything at first. But then they pull into a station, which is packed with horrible little monsters.  They decide to go into car 15.  It can't be worse than being devoured by a bazillion horrible monsters.  It's not.  There's two monsters and they kill them easily.  But now they have the problem of a train full of horrifying little monsters. Carl uses his protection spell.  It ends up smooshing everything behind them including trains 16 through 20 and all the mobs within. 

Ch 2 pg 19