Start walking at one end, as Facebook founder, chairman and chief executive officer Mark Zuckerberg often does. Intimate hallways pass between the conference-room clusters, then open out cinematically to expanses of desks, dappled with sun from skylights above—a high-tech forest. Your stroll passes snack kitchens with lounge seating where daylight pours in from 15-foot-high windows. End your walk at a cafe or cafeteria (three meals served daily, free)—more than a quarter mile later.