At first reading the beginning i was thinking this to be similar to one of my subs an underground prison as well. But on reading further I found this to be an entirely near complex adventure/ campaign that can be used as Muro stated. It is very feasible to have this dropped into an ongoing game for a respite from a current plot or to create an entirely different flow altogether.
I will have to follow the freetext for more information regarding this. It is near a complete sub as could be, although more information about the city would help me put it jus right. Kudos sir. Great work.