it sounds like an interesting premis for the game. I would make two suggestions, possibly.
1. While the whole nazi-thing might be best advoided, if we are going for the enemy group, we could perhaps use italians, if people are more comfortable with that. I do think at any rate it might be an idea to have some type of antagonist.
2. I'm not saying make the game into a "Myst" clone, (though i think that might be fun) but perhaps have more to the world then expected. SOmething might be going on in the shadows, or behind the scenes. Ie, perhaps the tried was once scientifically advanced many hundreds of years ago, but after the destruction it brought, they forsake it. Because of that there are still some forms of technology about, prhaps hidden bunkers, etc.
These are just ideas off the top of my head.
On a side note, i am curious as to whether we will be visiting just this world, or are there others planned?