Mark Twain was enchanted by Heidelberg, Goethe fell in love here, and composer Sigmund Romberg chose it as the setting for his much-loved operetta The Student Prince. Allied forces spared it during bombing raids and, after World War II, chose it as the location of the U.S. command headquarters, USAREUR. This combination of visitors (and in the case of the bombers, non-visitors) and romantic fancy has made Heidelberg almost a legend, vying with Munich as the most popular German destination for American travelers.

First-time visitors still fall quickly under the spell of this atmospheric old city, just as writers, the fictional prince and post-war GIs did. Today, international meetings and conventions fill the hallowed halls of Heidelberg’s university during the summer, creating new waves of devotees to spread its fame.

From the first glance, it’s easy to see why. Few cities have such an idyllic setting, nestled along both banks of the winding Neckar River, which has shaped steep hillsides as it carved a course through the rolling southwest German countryside north of Stuttgart, near the river’s junction with the Rhine. Halfway up the wooded slope behind the city’s old center looms the red sandstone façade of Heidelberg Castle, romantic in semi-ruin.

For five centuries the castle was the home of the Electors of the Palatinate, princely governors of this region, but was largely destroyed — along with most of the town — in the late 1600s by Louis XIV of France during the French-Palatinate War. Early in the 19th century, Frenchman Charles de Graimburg, who lived in the castle at the time, rescued it from a fate of slow demise and ultimate destruction. In the process, he saved more than 3,000 historic items, which subsequently formed the basis of Heidelberg’s municipal museum.

Most of Heidelberg’s old center dates from after the town’s destruction; its streets are lined with buildings from the 18th and 19th centuries. About 28,000 of its 135,000 residents are students at the University of Heidelberg — although on a lively Saturday evening it may seem as if students make up closer to 50 percent of the population. The university, one of Europe’s oldest (it dates from 1386) and most prestigious, gives the city much of its character — and its abundance of watering holes.

The university influences both economic and intellectual life and has made Heidelberg a major center for medical research for at least a century. The European Laboratory for Molecular Biology, the German Cancer Research Center, four Max Planck Institutes and the Academy of Sciences are here, and 2008 marked the ninth Nobel Prize winner culled from their ranks.

The combination of the university and decades of U.S. military presence makes it easy for English speakers to travel or do business here, and the Heidelberg Economic Development Agency actively promotes the city as a center for science, economics and capital investments, assisting foreign companies in establishing operations, sales or production facilities. Among the larger companies based here are Heidelberger Druckmaschinen, HeidelbergCement, Springer Science, LION Bioscience and Lamy, a manufacturer of writing instruments. The metropolitan Rhine-Neckar region, which includes Mannheim, Ludwigshafen and Heidelberg, was named Germany’s No. 1 innovations site in 2008.

USAREUR headquarters are tentatively slated to move about 50 miles north by 2012 or 2013, and if this happens it will deal a significant blow to the Heidelberg economy — a $63.6 million blow, to be exact. But even without the U.S. military, Heidelberg will continue to draw Americans to its historic streets, rollicking beer halls and romantic ruins.

Diversions

Heidelberg Castle draws like a magnet, a brooding pile half in ruin, suspended in leafy gardens above the Altstadt (Old Town). Climb the winding Burgweg (it’s a much better approach than the touristed Neue Schlosstrasse) or take the Bergbahn cable car (Bremeneckgasse, tel 49 6211 513 2150) to reach it, and wander in its gardens and courtyards. These are open all hours and are more interesting than the guided tours of the interior. The fascinating little Apothecary Museum inside is separate, as is the famous Grosses Fass, a giant — but empty — wine barrel.

For the best views of the castle and Altstadt, put on sturdy shoes and cross the Old Bridge, turning left up the Schlangenweg to follow the Philosophenweg (Philosophers Way), the famous path described by Mark Twain and the poets who frequented Heidelberg in the Romantic Era. It climbs from a very wealthy section of 19th-century mansions along the north side of the river and along the hills behind it. For views of the riverfront buildings and the scenic Neckar Valley, cruise on Rhein-Neckar Fahrgastschifffahrt (Untere Neckarstrasse 17, tel 49 6221 20181).

The Hauptstrasse is the pedestrian main street of Heidelberg’s Altstadt, one of Germany’s longest and lined by little shops (open 10 a.m.–8 p.m. weekdays, 9 a.m.–4 p.m. Saturdays), student drinking spots and cafés. Café Knösel, Heidelberg’s oldest, still makes the original Heidelberger Studentenkuss, a traditional chocolate candy with a romantic legend (Haspelg. 20, tel 49 6221 7272 75). For a sense of the university’s place in local culture, stop in at Schnookeloch, an authentic student inn that’s as popular with 21st-century students as it was with their predecessors (Haspelgasse 8, tel 49 6221 138 080). Live jazz, rock and blues begin at 9:30 p.m. Wednesday through Saturday nights at Jazzhaus HD, a club located in a 17th-century beer cellar (Leyergasse, tel 49 6221 433 2040). It’s a little out of the way, but the residential neighborhood of Handschuhsheim is not only a pleasant area to stroll, but its back streets are the place to find local bars, cafés, beer gardens and restaurants frequented by locals.

Follow the region’s 600,000-year history at the Palatinate Museum, in the Morass Palace (Hauptstrasse 97, tel 49 6221 583 4020) and take a look at the Student Prison, covered in irreverent graffiti from a century ago. More poignant for its history is the childhood home of Friedrich Ebert, the tailor’s son who became the first president of the short-lived German Republic in 1919 (Pfaffengasse 18, tel 49 6221 9107). Seasonal events worth considering are the Heidelberger Frühling music festival in late April into May, fireworks from the castle May through July, Christmas on Ice in Karlsplatz and the festive Christmas Market that fills the streets from late November to Christmas.

Info To Go

Frankfurt Rhein-Main Airport (FRA) is 50 miles north of Heidelberg. Lufthansa Airport Shuttle (tel 49 6221 651 620) leaves Terminal 1 almost hourly ($20, 75 minutes to Heidelberg). TLS (tel 49 6221 770 077 ) provides door-to-door service by van ($45) or private chauffeured car ($220). Major car rental firms are at the airport. Within the city, RNV buses and trams connect major points. A Heidelberg Card combines transit with free entrance to most sites. Visit www.heidelberg-tourismus.de.

Lodging

Der Europäis che Hof Hotel Europa
Owned by the same family for three generations, this elegant and stylish lodging is a member of the Leading Small Hotels of the World. Friedrich-Ebert-Anlage 1, tel 49 6221 5150, $$$$

Hotel Holländer Hof
The castle, boat rides on the Neckar, downtown streets and the Congress Center are a short walk from this elegant old riverside hotel. Neckarstaden 66, tel 49 6221 60500, $$$–$$$$

Hotel Zum Ritter St. Georg
This ornate 500-year-old Renaissance landmark is one of few buildings to survive the destruction of the town in the late 1600s. Hauptstrasse 178, Heidelberg, tel 49 6221 1350, $$$–$$$$

Dining

Alt Hendesse

If weather allows, don’t miss the experience of sampling traditional German dishes in a beer garden; this is one of the best. Mühltalstrasse 4 (Handschuhsheim), tel 49 6221 480 517 $$

Schwarz Das Restaurant
Sleek lines and blue lights make he contemporary setting memorable, and the world-beat menu draws raves for flavor and artistic presentations. Kurfürsten-Anlage 60 (Bergheim), tel 49 6221 757 030 $$$–$$$$

Simplicisimus
Art Nouveau interior, a private courtyard in summer and inspired innovative cuisine make this a good choice for a romantic evening or entertaining associates. Ingrimstrasse 16-D, tel 49 6221 183 336, $$$$