I am maintaining one application in construction industry space. That application was created 25 years ago by construction worker that never wrote single line of code before, but because he caused a lot of problems on construction site they give him Programming 101 book and let him build it.

15 years later the app was close to half milion lines long of huge bowl of spaghetti code. Only comments in whole codebase were timestamps. I don't know why he dated his code, but I find it fascinating: he never deleted basically anything so you can find different timeframes of when he discovered various concepts. There is use-exception-instead-of-if period, there is time when he discovered design patterns, there is time before he learnt SQL so all the database queries was done by iterating over whole tables and such. I am sure I will find commented Hello world somewhere in the code someday.

I am working on this codebase for 10 years. Code quality improved and major issues get fixed, but there is not enough budget to actually rewrote whole system, so after all it is more or less huge spaghetti monster and I get used to it.