For nine years during the Vietnam War, approximately 23,000 Laotians hid from American forces in the Viengxay caves, creating an elaborate city—complete with a hospital and a theater—in the 486 limestone caverns and 155 miles of tunnels. Seven of the caves have been opened to the public. English-speaking guides lead three-hour walking or biking tours, during which you'll see the dwellings of former Communist leaders, still stocked with uniforms and emergency oxygen pumps. Lao Air (lao-air.com) runs twice-weekly 80-minute flights to Xam Nua, in the Houaphanh province, from Vientiane. 011-856/64-314-321, from $3.