View across the Danube in Budapest during winter daylight, with riverside walkway and pedestrians in the foreground and pastel-coloured buildings and hills of Buda lining the opposite bank under a pale sky. Four cities, one river, and four very different personalities. The Danube might tie them together on a map, but in real life, Vienna, Bratislava, Budapest and Belgrade could not feel more distinct. These are some of the most fascinating Danube cities, and while I didn’t...