Sakai, a harbor city located just south of Osaka on Osaka Bay in Japan, is renowned for the Mozu Kofun—large ancient burial mounds. At the heart of the city, encircled by three moats, lies the colossal, keyhole-shaped Daisen Kofun, the 5th-century burial site of Emperor Nintoku. The hexagonal Old Sakai Lighthouse, dating back to 1877, stands sentinel over the harbor.