e.g. Super Mutant Ninja Turtles, the Mario games, numerous 90s action shows where the characters need to travel unseen underneath a city (although I guess for a lot of these shows these are actually storm drains, like the 50s movie Them!)
I know some ancient sewer systems had the walkways on the sides that are commonly depicted. Did the Romans feature the Cloaca Maxima in any of their stories or poems?
"It was in the sewers of Paris that Jean Valjean found himself" is the opening line of Les Miserables from 1862. The entire first chapter occurs in the sewer.
Keep in mind that the separation of sanitary sewer from storm sewer is a relative recent invention, made necessary to better treat waste water discharge. "Combined sewers" made more sense when the stormwater tended to contain lots of horse poop. They still tend to overflow their treatment facilities in heavy rains.