The Venetian Castle of Naxos, or Kastro, is a 13th-century fortress built by Marco Sanudo in the Old Town of Naxos, Greece. Located on a hill overlooking the Aegean Sea, it features medieval architecture, narrow alleys, and historic structures like the Catholic Cathedral and the Archaeological Museum of Naxos. Visitors explore its atmospheric streets, enjoy panoramic views, and delve into the island's Venetian past.