Rhodes. Greece. Partial view of the ruins of Monolithos, a ruined medieval crusader castle. Monolithos is perched atop the enormous crag called Monopetra on the west coast of Rhodes Island. Built by the Knights of St John in 1476, the once impregnable fortress is home to a 15th century whitewashed church of Agios Panteleimon and ruined basilica. Great views of the wild island landscape and wild coastline are on offer and the castle is easily reached by tourists. The island of Rhodes is the largest of the Dodecanese Island group and one of the most popular Greek Islands.