Margaret Island, or Margitsziget, is a popular recreational area in the middle of the Danube featuring restaurants and landscape parks. These medieval ruins are a reminder of the island’s importance as a religious center. The convent was built by Béla IV, King of Hungary and Croatia between 1235 and 1270, and Duke of Styria from 1254 to 1258. Presently only ruins are left, however, they contrast with the modern landscape making them a very popular location among photographers for their romantic charm.
About the source: Atlas Obscura
Atlas Obscura aims 'to inspire wonder and curiosity about the incredible world we all share'. You can contribute to their collection on their website.