Please help me find this movie again. I'd been searching for it for years and about a year or two ago I actually came across it on here (so I hadn't been remembering a weird dream or something!) but didn't buy it because it was really rare and didn't find anywhere that would ship to me or something (It may have been a foreign movie dubbed or something? I don't think so though.)Well, now I can't recall the name but I have a very vivid memory of one scene...
A kid is going up a dark mountain to sneak into a cave like room to get a sword (some sort of quest.) I also remember either the kid or someone else trapped in a deep dungeon like room in the mountain with a high window. It also may have involved a trip to an alternate time/place from modern times.
I wish I could remember more but if anyone has even a vague idea what movie this may be let me know. Thank you!

Possibly Mio in the Land of Faraway