There is an old film "Elvira: Mistress of the Dark". A modern girl inherits an old house and a cookbook from her deceased great-aunt. First, she doesn't understand what's that all about and just trying to settle in this quiet little town. After several attempts to use the cookbook for... well... cooking, she realizes that her great-aunt was a powerful witch...
Something like that will do, I think. Maybe even creating a spellcaster who doesn't know about being a spellcaster. He never enters a portal and learns everything about magic from experimenting.
