What I want to do:

I want a small map inside my main map where you see a small overview map about the level. But only areas you have visited before are shown, the rest is black. The mini map must correspond with the main level, because you can use teleport spells to move inside the map and you'll be automatically moved in the level. When saving a game, the info about the "discovered" areas must be saved, too.

I have some ideas to realize this, but all of them are quite very complicated and so I want to ask if somebody has a tricky idea how to solve this topic.