Budapest is the capital of Hungary. As the largest city of Hungary, it serves as the country's principal political, cultural, commercial, industrial, and transportation centre. In 2010, Budapest had 1,721,556 inhabitants, down from its 1980 peak of 2.06 million. The Budapest Commuter Area is home to 3,271,110 people. The city covers an area of 525 square kilometres (202.7 sq mi) within the city limits. Budapest became a single city occupying both banks of the river Danube with a unification on 17 November 1873 of right (west)-bank Buda and Óbuda with left (east)-bank Pest. Budapest is one of Europe's most delightful and enjoyable cities. Due to its scenic setting and its architecture it is nicknamed "Paris of the East".

Bucharest is the capital city, cultural, industrial, and financial centre of Romania. It is the largest city in Romania and was first mentioned in documents as early as 1459. Since then it has gone through a variety of changes, becoming the state capital of Romania in 1862 and steadily consolidating its position as the centre of the Romanian mass media, culture and arts. Its eclectic architecture is a mix of historical, interbellum, Communist-era and modern. In the period between the two World Wars, the city's elegant architecture and the sophistication of its elite earned Bucharest the nickname of the "Little Paris of the East".

Serbia, officially the Republic of Serbia, is a sovereign state situated at the crossroads between Central and Southeast Europe, covering the southern part of the Pannonian Plain and the central Balkans. Relative to its small territory, it is on the crossroads of European history and as such, it is a mix of cultures, ethnicity and religions. Also a landlocked country, its people, contrary to a recent stigma, are one of the most hospitable and welcoming During the summer tourists love spending their time in Belgrade and enjoy the nature of many national parks throughout the country. In winter, they are warmly welcomed to mountain resorts (one of the most popular being Kopaonik, featured on BBC as one of the best ski destinations in Europe). There are also many spa resorts such as Sokobanja, Niška Banja and Vrnjačka Banja.

Ruse is the fifth-largest city in Bulgaria. Ruse is situated in the northeastern part of the country, on the right bank of the Danube, opposite the Romanian city of Giurgiu, 300 km from the capital Sofia and 200 km from the Bulgarian Black Sea Coast. It is the most significant Bulgarian river port, serving an important part of the international trade of the country. $$https://www.youtube.com/watch?v=ah8TMe6HpuQ$$

Kalocsa, one of the oldest towns in Hungary, in Bács-Kiskun county, is situated in a marshy but highly productive district, near the left bank of the Danube River. Historically it had greater political and economic importance than at present. It is the Episcopal see of one of the four Catholic archbishops of Hungary. Amongst its buildings are a fine cathedral, the archiepiscopal palace, an astronomical observatory, a seminary for priests, and colleges for training teachers. The residents of Kalocsa and its wide-spreading communal lands are chiefly employed in the cultivation of paprika, fruit, flax, hemp and cereals, in the capture of waterfowl and in fishing.