A set of headlights on the Serbian side of the Danube River disappeared into a tunnel and emerged, and I had to remind myself that it was I — not the land — that was drifting by. In that moment, I was as carefree as a leaf on a stream, a stream called the Danube.

It was Day 10 of our 12-day cruise last fall on the river from Vienna to Giurgiu, Romania, followed by several days in Istanbul. It was an excursion into another world, another history and another humanity, distinctly different from and more diverse than anything my wife, Sandy, and I were expecting.

Danube River cruise: A June 29 article about a Danube River cruise said that, from the vantage point of the cruise vessel, the Pest portion of Budapest was on the right and Buda was on the left. Cruising south on the Danube, Pest is on the left and Buda is on the right. —

The river is the only constant in this corner of the world, the countries war-torn and orphaned by failed regimes, their peoples separated by culture, ethnicity, language and even currency.

Vienna, Days 1-3

We arrived in the early afternoon and checked into our hotel: UniWorld's River Duchess. The opportunity to shower, nap and unpack made all the difference in how we were able to reset our clocks and begin our vacation.

On our first full day in Vienna, we marveled at the architecture, toured the sites, walking mostly, and lounged in the Demel coffeehouse, indulging in pastries and espresso to the strains of Mozart and Beethoven.

By the second day, we had established an ideal vacation routine: breakfast, walking tour, local lunch, shorter walking tour, then back to the boat for a nap before cleaning up for dinner, the social highlight of the day.

The daily dinner specials included meat, fowl and fish, much of it indigenous; complimentary red and white wines were served with lunch and dinner. (Starting this year, cocktails also are complimentary on all of UniWorld's ships.)

We spent our last night here at Mozart Hall attending a concert of Strauss and Liszt that had been arranged for us in this Baroque masterpiece. It was more than we could have hoped for.

Budapest, Hungary, Days 4-6

We arrived midday, gliding beneath Budapest's famous bridges, with Pest to our right and Buda to our left. We had seen pictures, had read articles, had known people who had lived here, but nothing could have prepared us for the splendor of this city.

Over the next day and a half, we toured its two distinctive halves: Buda, the hilly, more subdued and artistic side with spectacular vistas from Matthias Church; and Pest, the flat, commercial side with its churches, synagogues and public buildings.

It was in Pest that we experienced Soviet Baroque, the locals' name for the utilitarian buildings of the former Eastern Bloc. Each had its own sad story of abandonment, indeterminate ownership and imminent collapse.

It was here that we had our first brush with the currency conundrum. Although Hungary and the countries downstream are members of the European Union, many have not yet qualified as currency members. All accept euros and most accept U.S. dollars, but expect to receive change in the local currency, which is virtually useless beyond its borders.

Daylight drab gave way to the dazzling jewel that is Budapest at night, its streets, buildings and bridges lighted up beneath a clear, cool sky.

We sailed past the huge Parliament Building on our way of town, its illuminated arches and spires reflected in the Danube in a scene surreal and magical. It remains the most memorable image of our trip.

En route