If you've ever wondered how Roman emperors lived, arrange a walking tour of Diocletian's Palace in Split, Croatia. Originally built by emperor Diocletian in the late 3rd century, this massive complex of buildings, nearly a quarter kilometer long, was built as a retirement palace for the emperor. Now in use as a combination of shops, restaurants, and a few homes, this spectacular UNESCO World Heritage Monument is located in the center of the city. Filled with soaring columns and towering arches, this palace will give you a view into the level of extravagant luxury that the ruler of one of the largest empires in history could afford to build himself as a retreat in his old age.