Beloeil Castle, the ancestral home of the prince de Ligne, has been called, with some justification, the "Versailles of Belgium." It is, quite simply, magnificent. The castle sits amid French-style gardens in its own park, on the shores of an ornamental lake. For more than a thousand years, the de Ligne family has lived in the grand style that pervades these vast rooms, filled with priceless antiques, paintings by the Masters, historical mementos (among them a lock of Queen Marie Antoinette's hair), and more than 20,000 books, many of them rare editions.