I’ve been up only a couple times – one was a long cab ride to meet a ‘friend’ back in the day, one was playing the 2-beers-hop bus game, getting off after two are done, buying 2 more, getting on next random bus, seeing where you end up. I would agree with Charlie that for writing purposes, just mentioning the north train station probably brings up the most vivid and universally understood implications of dangerous, poverty-stricken, downtrodden, and overall sleazy.
That sounds like a fun game. I’m sure there are some really grimey areas in the North, but I also am not very familiar with them by name. Like 99% of foreigners in Chengdu, I live far from that part of the city and never go there.