The moment you spot red tile-roofed Dubrovnik from your Holland American Line ship, you’ll understand why the UNESCO-designated Old Town is called the “Pearl of the Adriatic.” A Mediterranean cruise with Holland America Line introduces you to Croatia’s many other charms as well, from the Roman-built Diocletian’s Palace in Split — another UNESCO World Heritage Site — to the lavender-scented island of Hvar and Rijeka for tours of the 13th-century Trsat Castle and a family-owned olive oil estate.