I remember reading somewhere that there is a word in old Norse for unwise/foolish that etymologically refers to someone who's not travelled or left home. Any ideas?
You are probably thinking of Icelandic heimskur "stupid, foolish", which comes from Old Norse heimskr "foolish, silly; who has never been from home" (from ON heima "home"). It appears frequently in Norse sagas, sometimes in the intensive form allheimskr "very stupid". A famous instance of this is the saying "Engi er allheimskr, ef þegja má" ("No one is a total fool, if one knows when to be silent") in the Saga of Grettir the Strong.
I am not aware of an opposite word relating wisdom with being well-travelled, though.