of the city. Parts of the city (mainly the Naval Port) have been declared a UNESCO World Heritage Site. In October 1981 the Whiskey-class Soviet submarine S-363 (known as "U137" in Sweden) ran aground in the archipelago near Sturkö just outside Karlskrona. The media characterized it as the "Whiskey on the Rocks" affair. The incident caused a temporary rise in tensions between Sweden and the Soviet Union. While the submarine's grounding was inadvertent, and likely the result of inebriation among the crew, the submarine almost certainly was engaged in an unspecified covert mission at the time. Geography The city of Karlskrona is spread over 30 islands in the eastern part of Blekinge archipelago, Trossö being the main one. Other populated mentionable islands are Saltö, Sturkö, Hästö, Långö and Aspö. The islet of Stumholmen was formerly property of the Navy and today it houses the National Naval Museum (Marinmuseum). Outside the city lies the archipelago of Karlskrona, the most southern of the Swedish archipelagos. Several islands are connected to the city by ferries. Culture and heritages The most important day in Karlskrona is the day before midsummer's eve. On that day a big fair takes place and attracts tens of thousands to visit Karlskrona. The fair is called Lövmarknaden (The Leaf Fair) and is very popular among the locals. The main square of Karlskrona is the biggest in Scandinavia. Every year in late July/early August a popular festival called The Sail takes place in the harbor of Karlskrona. Usually it is a place where families go to have something to eat and drink, and perhaps watch the sailing boats lined up at the pier. During the sail, the seascouts of Karlskrona will row a boat carrying torches along the docks while playing the national anthems for the visiting ships. Lately The Sail has been replaced with a festival called Skärgårdsfest. The old architecture together with the naval installations comprise the major tourist attractions of Karlskrona. The city has a pleasant atmosphere and is one of the highlights of south-east Sweden. Architectural Heritage Karlskrona has preserved its buildings and its layout virtually intact since its foundation. When the city was founded in 1680, it was primarily thought of as a military city, with many defenses and fortifications exploiting the particular topography of the city. Some fortifications were located on the main island (Trossö) such as the Bastion Aurora, built at the beginning