We continue our celebration of National Park Week (through April 24)–and the UNESCO International Day for Monuments and Sites–with a visit to the impressive Square Tower House in Mesa Verde National Park. Square Tower House is one of many cliff dwellings constructed by the Ancestral Puebloans in what is now the American Southwest. At 27 feet, it"s the tallest structure in the park. Square Tower House is also notable for its kiva, a round, sunken room used for ceremonies. Unlike most of the ancient kivas found in the region, the kiva at Square Tower House has an intact original clay roof supported by wooden beams.