Bosanska Dubica to shorten the travelling time to Zagreb. The other one is to the east heading towards Doboj and connecting Bosanska Krajina to the important Corridor Vc in Bosnia and Herzegovina. Banja Luka International Airport is located 23 km from Banja Luka. There are two airlines currently, B&H Airlines and Adria Airways, with regular flights to Ljubljana (four times weekly) and Zürich (three times weekly). Charter flights also operate from the airport, and the airport can be used as a back-up to Sarajevo Airport. Zagreb Airport, due to weather conditions in winter often preferable to Sarajevo, is approximately two hours away from Banja Luka by car. Željava Air Base, situated on the border between Croatia and Bosnia and Herzegovina under Plješevica Mountain, near the town of Bihać in Bosnia and Herzegovina, was the largest underground airport and military airbase in the former Yugoslavia and one of the largest in Europe. Prijedor also has an airfield in the north-eastern part of the city in the area of Urije. The airfield has a fleet of light aircraft and sailplanes. The airfield was used by the Yugoslav partisans and was the first operative partisan airfield during World War II. The airfield also serves as the home of the city's renovated Parachuting club. Bosanska Krajina is the hub of the railway services in Bosnia and Herzegovina, comprising more than one-half of the railway network of Bosnia and Herzegovina. Services operate to the northern and western Bosnian towns Banja Luka, Prijedor, Bosanski Novi and Bihać. The rail network also operates to Zagreb (twice daily), and Belgrade. Gallery Historical gallery See also Krajina Regions of Bosnia and Herzegovina Turkish Croatia References Sources Historical regions of Bosnia and Herzegovina Ottoman period in the history of Bosnia and Herzegovina Regions of Bosnia and Herzegovina History of Bosanska Krajina