"Yes, George Washington slept here. But so did Liz Butler, and that was much more important to Robin Richardson Greenhalgh. Growing up in this stately stone farmhouse near Berryville, Va., Greenhalgh's slumber parties with her third-grade friends were a bigger deal to her than the sleepovers of a Founding Father. "'To me, it was just our house,' said Greenhalgh, 54, looking around the spacious entry hall of Fairfield, her family's home for seven generations. It is remarkably well preserved after welcoming visitors, both grand and giggling, for longer than this country has been a country. 'I really didn't appreciate its remarkable heritage until much later.' "But now that Greenhalgh fully celebrates the heritage of a house that was built by George Washington's first cousin and later owned by Robert E. Lee's aunt, she is preparing to say goodbye to the Clarke County estate. Citing the time and cost of maintaining a colonial mansion, Greenhalgh has put Fairfield on the market - even though that leaves her, and preservationists, anxious about the fate of one of Virginia's great unsung historic estates." On the market: Va. estate with a hefty history