An impressive set of military structures between the Baltic Sea and Lake Liepāja and Lake Tosmare.  Construction of the fortress began in the late 19th century on the basis of a decree by Russian Tsar Alexander III, and it cost 45 million gold roubles.  The fortress includes accommodations and elements of fortifications – sites for cannons, trenches, gunpowder cellars, systems of canals, a narrow-gauge rail line, etc.  In 1908, the fortress was shut down because of a change in Russia’s defence concept, and the construction of it was declared to have been a strategic mistake.  There were attempts to blow up the underground structures and cellars during World War I, but that did not really succeed.  Some elements of the fortress were of great importance in Latvia’s liberation battles.  Surviving today are the Northern forts, the Central fort, the Eastern fort, the Southern fort, the shoreline defensive batteries (No. 23, 3), Redāns, Lunete, and others.  Most are not improved, so visits may be dangerous.  The northern part of the fortress includes the Military Port, which has experienced seven different armies and regimes. During the Soviet years, it was closed to civilians.  There are many outstanding monuments to military history.  Tourists love the Karosta prison, which offers educational programmes.