of the best preserved medieval towns in Europe and the authorities are continuing its rehabilitation. Major sights include the Town Hall square (), the city wall and towers (notably "Fat Margaret" and "Kiek in de Kök") as well as a number of medieval churches, including St Olaf's, St. Nicholas' and the Church of the Holy Ghost. The Catholic Cathedral of St Peter and St Paul is also in the Lower Town. Kadriorg Kadriorg is east of the city centre and is served by buses and trams. Kadriorg Palace, the former palace of Peter the Great, built just after the Great Northern War, now houses the foreign art department of the Art Museum of Estonia, the presidential residence and the surrounding grounds include formal gardens and woodland. The main building of the Art Museum of Estonia, Kumu (, Art Museum), was built in 2006 and lies in Kadriorg park. It houses an encyclopaedic collection of Estonian art, including paintings by Carl Timoleon von Neff, Johann Köler, Eduard Ole, Jaan Koort, Konrad Mägi, Eduard Wiiralt, Henn Roode and Adamson-Eric, among others. Pirita This coastal district is a further 2 kilometres north-east of Kadriorg. The marina was built for the Moscow Olympics of 1980, and boats can be hired on the Pirita River. Two kilometres inland are the Botanic Gardens and the Tallinn TV Tower. == Transport == City transport The city operates a system of bus (73 lines), tram (4 lines) and trolley-bus (4 lines) routes to all districts; the long tram system is the only tram network in Estonia. A flat-fare system is used. The ticket-system is based on prepaid RFID cards available in kiosks and post offices. In January 2013, Tallinn became the first European capital to offer a fare-free service on buses, trams and trolleybuses within the city limits. This service is available to residents who register with the municipality. Air The Lennart Meri Tallinn Airport is about from Town Hall square (). There is a tram (Line Number: 4) and local bus connection between the airport and the edge of the city centre (bus no. 2). The nearest railway station Ülemiste is only from the airport. The construction of the new section of the airport began in 2007 and was finished in summer 2008. Ferry Several ferry operators, Viking Line, Tallink and Eckerö Line, connect Tallinn to Helsinki, Mariehamn, Stockholm, and St. Petersburg. Passenger lines connect Tallinn to