All the houses described are within several hours’ drive of New York City. Some are open year round; most are open April to October; at all you are led through by a guide. Heading north from the city, you would reach them in this order: Sunnyside (914-631-8200), Lyndhurst (914-631-0046), Philipsburg Manor (914-631-8200), Washington’s headquarters (914-562-1195), the Mills Mansion (914-889-4100), Clermont (518-537-4240), and Olana (518-828-0135). For general tourism information, call the Hudson River Valley Association (914-265-3066). A good introduction to the area, containing history, information on all these houses and many more, and recommendations for places to sleep and eat, is The Hudson River Valley: A History & Guide , by Tim Mulligan (Random House, 1985). For general history, start with Life Along the Hudson , by Allan Keller (Sleepy Hollow Restorations, 1985). Two especially noteworthy houses not mentioned in this article, the Franklin Roosevelt and Frederick W. Vanderbilt homes at Hyde Park, were written about by Geoffrey Ward in the April 1987 issue of American Heritage. Another place to visit in the area is, of course, the U.S. Military Academy, at West Point.