It's a beautiful area, there's a lot of history in Fayette County. You should also check out Kentuck Knob - that's another Wright house that's fairly close, just not as famous. I think there are also quite a few B&Bs around there that you could stay at.
Fallingwater is kind of funny for me, it's so beautiful on the outside. I haven't been there for years, but was struck by the interior - different than what I expected. I'd be interested to hear what your impressions of it are.
If you have time, take a drive in the area on the Old National Road/aka "Old Route 40". You could always check out Fort Necessity (it was so small, how did *anyone* make it out alive?), the surviving toll-houses, the Inns that are still standing. I've also heard great things about the restaurant Chez Girard in Hopwood and Hopwood itself has more original early 1800s stone/historical buildings than many more famous towns.
Yeah, I know a lot about the area

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agnes!