In fact, from the late seventeenth century, a messenger of King Louis XIV of France discovered underground citadels and churches on the Cappadocian plateau. He returned to Europe to declare this important discovery, but no one believed, everyone thought he was crazy. Poster Classroom Social Distancing Greetings. Less than a century later, the more people discovered the citadels and underground mosques, it was when the Cappadocia region gradually became famous. The pilgrims to the holy land as reunited, archaeologists also spend countless efforts with this land. However, how the underground citadels were built and where the earliest inhabitants living here came from and where they went is still an unanswered mystery.