Ooh, I just found this thread and have to post too. I spent the past six months in Germany, and in early November I dragged a friend with me down to Munich and Bavaria to go on a Gabriel Knight geek-tour. We went to look at Castle Neuschwanstein (which is very small, but you recognize a lot in it from the game), Marienplatz and a few other places from The Beast Within, and I can really recommend the trip. Bavaria is extremely beautiful! I especially loved Starnberger See, which is where the Ludwig memorial can be found. We had to walk for over an hour to find the cross and the sanctum, but it was totally worth it.
In any case, I'm posting links here to a few of the pictures I took that I hope at least the other GK crazies will appreciate (we also visited the Ludwig museum, but you're not allowed to take pictures inside of course, so there is no photographic evidence). I didn't get them quite as freakishly identical to the game screens as tsa did, but if you've played the game you'll probably be able to recognize the places in question...
Marienplatz:
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Ludwigs Totesort:
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Schloss Neuschwanstein:
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For my next geek-tour I'm thinking I'll do GK3.