Organ music wafting outside the Gothic Church of the Holy Ghost here is invaded by the daily chimes of Town Hall Tower and a cacophony of clocks striking the hour.
The sounds of Bach sift gently under the scents of flowers and fish on sale at the open-air Marktplatz. A glockenspiel plays folk melodies. Street musicians compete with antique store window displays for crowd attention.
As we stand smack dab in the heart of this baroque Old City, the ruins of Heidelberg Castle - for five centuries the glittering residence of the Palatinate prince electors - peer eerily over our shoulders. In front of us is the ever-somnolent Neckar River, churned slightly by a small dam upriver and carrying everything from swans and kayaks to slow-moving barges. In every direction are mountains, forests, vineyards.
This is indeed romantic Germany.
The vendors' cries and fountain splashes that echo out of this market on the Hauptstrasse (main street) became my favorite memories of Heidelberg. But they were not on the list of three main reasons that 550,000 tourists flock here each season, as I found on my next day's guided tour of the city.
Those reasons are the castle (until 1803 the home of German emperors); the University of Heidelberg, the oldest university in Germany (1380); and the area's heritage as home of Germany's Romantic movement.
Poets, writers, artists, and musicians flocked here in the early 1800s to overthrow the French culture that had dominated Germany since the Thirty Years' War (which ended in 1648). The castle, long out of favor because it was not in keeping with the rococo age, became German Romanticism's new symbol. ''With its old moats, jagged turrets, and memories of court troubadours,'' writes Harry B. Davis in ''What Happened in Heidelberg,'' ''it epitomized the medieval spirit which the Romantics sought to recall to life.''
It was here, then, that old country sagas and folk tales were revived. Old German paintings were rediscovered and German songs and music studied afresh. Artists painted the plush, wooded landscapes, and poets penned anew.
Since Romanticism led to the emergence of a German national consciousness, a host of songs and poems were dedicated to the movement's birthplace, Heidelberg. Those included Matthisson's ''Elegy'' (1796) and Holderlin's ''Ode to Heidelberg'' (1799). Goethe visited the city eight times and lost his heart to Marianne von Willemer, who composed a poem in 1824 in memory of their meeting. Carl Maria von Weber was inspired to write his opera, ''Der Freischutz,'' Robert Schumann turned from painting to composing, and Sigmund Romberg composed the music for ''The Student Prince.''
The list goes on and on. But it was the Romberg operetta that made Heidelberg perhaps the best-known German city among Americans. ''The Student Prince,'' first produced in 1924, became more successful on Broadway than anywhere in Germany.
The best way to see the modern remains of what stirred the German Romanticists is the guided bus tours that leave daily from the Bismarckplatz at the Old City's edge at 10 a.m. and 2 p.m. When you're through, you'll want to take a walking tour of the Old City, taking in as many sights as you can; and don't miss Philosophers' Walk, a hillside promenade on the opposite bank of the Neckar.
The castle is a must, of course, as is the funicular cable car that goes well beyond the castle up to the Konigstuhl observatory, where you can see for miles.
Don't worry when you see the Woolworth's while waiting for your tour bus at Bismarckplatz. This part of the city is ''new'' Heidelberg. Until 1880, our guide says, it was a large meadow. The Old City and Old University stretch about a mile in the other direction and are protected by architectural laws banning any new buildings.
Over the past 20 years, over 250 million deutsche marks (about $125 million) has been spent on renovation of town and university buildings. Other major changes in the past decade include making main street a pedestrian mall, building underground parking garages, and diverting the tram cars around the Old City.
The director of tourism here told me the proliferation of schnell imbiss (fast food) restaurants is one of the most noticeable changes in Heidelberg over the last 10 years - traceable to the large student population and frequent visits by school-age groups from all over Germany.
Our guide begins the tour by telling us Heidelberg was not bombed during World War II (as was nearby Mannheim) because the Americans wanted to live there after the war. She says the Americans even dropped leaflets at the time carrying a message to that effect.
Outside the Old City, we pass the portland cement factory, one of modern-day Heidelberg's industries. Another is medical research, and a large facility was started here in the 1950s with help from the Rockefellers.
From the opposite side of the Neckar, many of the Romantic artists stood their easels to paint the castle, Alte Brucke (old bridge), and quaint clock towers of the cityscape. You can see the section of the old bridge that was bombed by the Germans themselves to prevent the American troop advance in 1945.
Today, boat racing, sailing, and pedal boats are favorite pastimes along the river. Tourists take river cruises past the monastery upriver that once housed many artists, poets, and musicians. Today, a large sports complex has been built above the monastery.
The castle is a tour in itself. Don't miss the Renaissance facade of the Ottheinrich building or the great, wooden wine vat in the cellar (supposedly the largest in the world) or the Hall of Mirrors Building. The great gardens built by Friedrich V (the Winter King) were destroyed in the Thirty Years' War. But the Gun Park has a large garden of beautiful flower beds surrounded by the Electors' statues and theater ruins.
When you view the city from the great terrace of the castle, you can see why Heidelberg has the earliest spring in Germany. It is bounded by mountains on all sides that keep off the chilling winter winds. And that explains one of Heidelberg's proudest assets: asparagus in May.
Back to town for your walking tour, you have to see the Palatinate Museum. Here are the paintings of Michael Kunz, Ernst Fries, Carl Eggers, Albrecht Adam, Franz Kruger, Max Beckman; the jawbone of ''Heidelberg man''; and sculptor Tilman Riemenschneider's ''Christ and the Apostles'' in limewood.
Heidelberg is now a relatively quiet university town - besides being one of the hottest tourist locations in Germany, owing partly to its centralized location. A stone's throw from the busiest airport in Europe, Frankfurt, it's also situated right at one end of Germany's famous castle route on the Rhine River.
The population is 135,000, but 27,000 of those are students and 17,000 more are American GIs stationed at the United States Army's European headquarters. A recent study by the city of Hamburg found Heidelberg - with its riverside City Theater, its many concerts, museums, and festivals - to be the top city over 100 ,000 population for leisure and cultural activities in Germany.
The many cafes seem to add to a vibrant intellectual life fed by a university that is described as offering everything except veterinary medicine and agriculture. Stores close at 4 p.m., when the activity moves to the cafes - intense conversation and voracious reading of books, magazines, and newspapers.
I didn't sample the night life, which the city tourism director said does not approach that of large cities like nearby Mannheim or Munich, but has a character all its own. Clubs and discos are evident, however, with such names as Club 1900 and Alt Berliner Kneipe.
At the latter, I saw live jazz from a uniformed band on a Sunday afternoon.
''The Student Prince'' is one of the main attractions each season, performed in the castle courtyard every weekend from July 27 through August as part of Heidelberg's annual Castle Festival. If you plan to go, you might want to avoid the weekend of Aug. 5, when the Formula One Grand Prix race in nearby Hockenheim helps fill Heidelberg's 3,600 hotel and pensione guest beds.
When you visit, make a point to sample the great German pastry in the many Konditorei lining Hauptstrasse. The famous cafes are Knosel, Scheu or Schafheutle, and Garden. I heard that the best restaurants were near the Alte Brucke.
Following that advice, I had my best German meal in three weeks in Germany at Hollander Hof. The great food surprised me, because the small room looked like a restaurant for overflow patrons.
Later I tried a restaurant that looked great as well. It's called Merian-Stuben, and looks like a baroque palace on the river next to the City Theater. You can't miss it. And shouldn't.
For background information on the city, the best book in English is Harry B. Davis's ''What Happened in Heidelberg.'' Short, readable, and to the point, at 6 DM (about $3.)