From Wiki:
"Watchmen features a story within a story in the form of Tales of the Black Freighter, a fictional comic book from which scenes appear in issues three, five, eight, nine, ten, and eleven. The fictional comic's story, "Marooned", is read by a black youth in New York City.[23] Moore and Gibbons conceived a pirate comic because they reasoned that since the characters of Watchmen experience superheroes in real life, "they probably wouldn't be at all interested in superhero comics."
This story within a story was something I haven't seen before when I first read the comic.