Danube, the river that joins four capitals.

What is the Danube as a trip?

The second-longest river in Europe, after the Volga: about 2,850 km from Donaueschingen, in the Black Forest, where the Brigach and Breg streams join, to its delta on the Black Sea, between Romania and Ukraine. It crosses or borders ten countries, Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine, and passes through four capitals: Vienna, Bratislava, Budapest and Belgrade.

As a travel zone, the Danube is not a territory but an axis. You follow it by bike on an almost flat path, by scheduled boat or cruise, or by train between cities that face the river. The most visited stretch, and the one our pages cover, runs from Passau, on the German-Austrian border, to Budapest: about six hundred kilometres with Baroque abbeys, terraced vineyards, two imperial capitals and the bend of the river north of Budapest.

How do you travel it by bike, boat or train?

By bike, the Donauradweg, part of the EuroVelo 6 route, follows the river on one or both banks. Between Passau and Vienna it is about 320 to 340 km, almost without hills and with villages every few kilometres, and it is one of the busiest multi-day cycling routes in Europe. It is done in a week at an easy pace, with bike hire and luggage transfer between accommodation. From Vienna to Budapest it is another three hundred kilometres or so, with fewer services.

By boat, there are three ways. Multi-day river cruises go up and down between Passau, Vienna and Budapest, sleeping on board. Daytime scheduled boats cover short stretches, such as the Wachau between Melk and Krems. And the Twin City Liner catamaran links Vienna with Bratislava in about 75 minutes downriver, from spring to October; in the opposite direction it takes a little longer.

By train, it is the fastest between capitals: from Vienna to Bratislava, around an hour; from Vienna to Budapest, about two hours and three quarters on a direct train. Commuter trains reach river towns such as Tulln from Vienna, or Szentendre and Vác from Budapest. By air, from Spain there are direct flights to Vienna and Budapest, and often to Munich, the gateway to the German stretch.

What to see along the river?

In Germany, the Danube passes through Ulm, with the cathedral with the tallest steeple in the world; through Regensburg, whose medieval old town is a World Heritage Site; and through the Weltenburg Gorge, before reaching Passau, where the Inn and the Ilz join it.

In Austria, the river crosses the Wachau, about 35 km of vineyards and apricot trees between Melk and Krems, a World Heritage Site since 2000, with Melk Abbey at one end and Göttweig above Krems. Vienna is an hour away; before that, Tulln has the Egon Schiele museum. East of Vienna, Carnuntum was the capital of the Roman province of Upper Pannonia.

In Slovakia, Bratislava has the castle above the river and the ruin of Devín at the confluence with the Morava. In Hungary, the Danube Bend brings together Esztergom and Visegrád in a curve between hills, with Szentendre and Vác on the banks. Budapest closes the stretch with its two banks, the Parliament and the thermal baths.

Downriver, the Danube crosses Belgrade, narrows at the Iron Gates between Serbia and Romania and ends in a delta of channels and lagoons, a World Heritage Site since 1991, which is visited by boat from Tulcea.

When to go and what changes in each season?

May to September is the cycling and boat season. May, June and September are the best months: good temperatures for pedalling, green vineyards and fewer people than in high summer. In July and August it can be very hot in Vienna and Budapest. In late September and October the grape harvest arrives in the Wachau, although some scheduled boats already reduce their timetables.

In December the river cruises run Christmas-market routes between Vienna, Bratislava and Budapest. From November to March most scheduled boats stop and the cycle route loses services. In spring, and sometimes in summer after heavy rain, the river can rise and force boats to be suspended or stretches of the path to be closed.

How many days and how to divide them?

With a week, by bike, you do Passau–Vienna; by train, Vienna, Bratislava and Budapest, with two nights in each capital and an excursion to the Wachau or the Danube Bend. With ten days, you add the German stretch or a second excursion from each capital. For a long weekend, choose one city and its stretch of river: Vienna with the Wachau, or Budapest with Szentendre.

What is worth knowing before you go?

Austria and Slovakia use the euro; Hungary, the forint. All three are in Schengen. On the cycle route book accommodation in advance in May and June, when there are more cyclists. Check the season and timetables of the scheduled boats before counting on them, because they vary each year.