The most recognizable feature which defines the History of Dubrovnik and gives it its characteristic are its intact city walls which run uninterrupted for 1940 meters encircling the city. This complex structure, one of the most beautiful and strongest fort systems in the Europe is the main attraction to the city's visitors. Five fortresses, St. Lawrence and Revelin together with another three incorporated in the city walls, Minceta Tower, Fort Bokar and St. John's Fortress give to its visitors unforgettable views of the city. The Maritime Museum is divided into four sections; the period of Dubrovnik Republic, the age of steam, the Second World War, and the techniques of sailing and navigation, the exhibition displays maritime heritage of a wider local area since the Dubrovnik Republic through to today. The Aquarium is located at the first floor of St. Ivan's Fortress. In the 27 tanks various fish such as eel, red snapper, ray, sea bass, grouper, John Dory, etc. are exhibited as examples of the fish species from the Adriatic Sea. The Dominican Monastery and Museum has the museum with artifacts of Dubrovnik's goldsmiths, reliquaries and other sacral objects.