One of the things I found fascinating about the work of Joseph Campbell is the idea that a 'great flood' was a common idea / event across any number of cultures.

Historically it happened many times, certainly. Sometimes completely forgotten, sometimes a key component upon a peoples' mythology / history, and sometimes even elevated unto a massive fairy-tale, as with the Christian-Noah thing.

Rip Van Winkle was another fascinating one, but the examples go back way before Christianity et al, as scholars & historians have found.