If you were wondering why the streets of Dubrovnik aren't as busy as they normally are at this time of year, it’s a public holiday in Croatia today.
The 15th of August is the Assumption of Mary a Catholic holiday in many countries in the world. In Europe today is not only a public holiday in Croatia but also in Belgium, Austria, Cyprus, France, Greece, Italy, Luxembourg, Malta, Poland, Portugal, Romania, Slovenia and Spain.
The Assumption is important to many Catholic and Orthodox Christians as the Virgin Mary's heavenly birthday (the day that Mary was received into heaven).
For a full list of the public holidays in Croatia see this link