It could just as easily be the 1830s, when Peter Joseph Lenné transformed these nearly 500 acres of royal hunting preserve along the River Spree into a park. I resume walking, footsteps crunching on the glazed ground, and suddenly the world explodes in sound—thundering, heart-thumping sound that, after the first shock, proves to be music. Really bad, stupendously loud European disco music.

Practically vibrating as I walk, I emerge onto the broad Strasse des 17. Juni (named for the East German workers' uprising on that date in 1953). The handsome, formal avenue has been transformed into a carnival midway. In preparation for the following night's New Year's Eve celebration, stalls selling souvenirs, cotton candy, bratwurst, and, of course, beer have been set up along both curbs. A towering Ferris wheel turns lazily, and, just in front of the Brandenburg Gate, a broad stage has been erected with vast speakers on both sides. It is from these that the disco inferno, evidently on tape, is emanating. It is a wonder that the snow hasn't all melted. Then, as suddenly as it started, the music blessedly stops. I find another path into the now-silent woods and within 10 paces I have returned to the 19th century again.

Sony Center's site was a wasteland a few years ago.

After just two days here, I am becoming used to such jarring transitions, for Berlin is a metropolis of juxtaposition. Sonic, historic, political, cultural, commercial—in this city so celebrated for unification, there may no longer be a Wall but there is always another side.

From the architectural pyrotechnics of the newly reborn Potsdamer Platz to the graceful elegance of Museum Island and the Gendarmenmarkt, the city's loveliest square, to the grit and energy of the Scheu-nenviertel (the old Jewish quarter), with its galleries and bars, from the shadow of war and oppression to the promise of a new century, Berlin presents the visitor with a series of incongruities. The city insists on contradiction and confrontation.

Spend an hour or so admiring the Raphaels and the Vermeers in the Gemäldegalerie Museum in the Kulturforum, then walk a couple of hundred meters to the Mies van der Rohe-designed Neue Nationalgalerie and gawk at photographer Helmut Newton's life-size Big Nudes. Stroll down Unter den Linden, the city's most celebrated boulevard, to the beautiful space of Bebelplatz, framed by the facades of the State Opera, the Old Library, and the huge domed church of St. Hedwig. Then notice a small plaque in the pavement that reminds the visitor that it was here the Nazis burned books in 1933. Engraved on the plaque are Heine's words: "Where books are burned, in the end people will burn." Then, finally, cross Unter den Linden to where, in front of the iron gate of Humboldt University, a woman, her face flushed from the cold, is selling used books from a row of tables. "Yes, yes," she says, smiling and shrugging, when asked if she is aware of what went on in this same square less than 70 years before. "Of course."

Historically a city of conflict and polarization, Berlin has also always been a hotbed of ideas and creativity, a city that, as commentator Karl Scheffler put it nearly a century ago, is "always becoming and never managing to be." Even reunification—perhaps especially reunification—produces no unity of opinion. Remember the heady images on CNN from that November night in 1989? Ecstatic East Berliners pouring through the newly opened border crossings, waving and honking the horns of their sputtering little Trabants; West Berliners, weeping and cheering, greeting them in front of the Brandenburg Gate with hugs and champagne; hundreds dancing on the Wall itself or bashing at the concrete with sledgehammers. Well, more than a decade has passed since that party rocked the night, and Berlin seems still to be grappling with the tidying up.

"Too many people have come in," I am told by a surly taxi driver, as he guns his Mercedes past the refurbished Reichstag. Redesigned and streamlined by architect Sir Norman Foster, topped with a glass dome signifying transparency, the haunted old building is of course one of the principal destinations of some of those newcomers, specifically, the members of the German government, as Berlin has once again become the nation's capital. My driver, though, is referring to the East Berliners and the immigrants from Eastern Europe who have poured into the city since the Wall came down. Still, though he and many other former West Berliners openly resent the economic burden this influx has placed on the city, it is as clear as the dome we are passing that Berlin has once again become the place to be (or to visit) for a new generation.

"It is very treeendy here," says Michael Riemann, a student from Dortmund on a visit to the capital. Seated in a smoky trattoria just off Oranienburger Strasse in the Scheunenviertel, Riemann draws out the word, making quotation marks in the air with his fingers. "Germans look to Berlin as Americans do to New York. There is something in the air."

The "Berlin air" is a phrase that gets used a lot, and it refers to more than just the climate. Indeed, David Large, in his eminently readable new book, Berlin, quotes Conrad Alberti's 1889 novel The Old and the Young, in which the protagonist talks excitedly about the "nervous, endlessly quivering Berlin air . . . which works upon people like alcohol, morphine, cocaine, exciting, inspiring, relaxing, deadly; the air of the world city."

A F T E R   T H E    F A L L By Amy Graff When the Berlin Wall came tumbling down on November 9, 1989, my dad, like many people throughout the world, saw the event not only as a political triumph for Germany and an end to the Cold War but as a symbolic step toward freedom for people everywhere. An inveterate traveler, he wanted our family to witness history unfolding and booked a flight for us to visit Berlin that spring. I was only 15 years old, but I will never forget chipping away at the Wall with a hammer and my dad's explaining to me that six months earlier people who lived on the east side of the Wall could not walk into a department store and buy a pair of Levi's—the perfect object lesson in freedom for a curious teenager. The Wall's significance is rooted in history. As part of the Soviet bloc, East Germany began surrounding West Berlin with blockades on August 13, 1961, to stem the exodus of refugees. Eventually, a 95-mile concrete structure surrounded West Berlin. The divided city was center stage for the Cold War; the Wall became the foremost symbol of this ideological conflict. The Wall shut off nearly every person living in East or West Berlin from relatives and friends living on the opposite side. Olaf Kolbatz, a Berlin tour guide, says, "I lived in the East and my grandmother lived in the West. If the Wall hadn't been there, I could have walked to my grandmother's house in five minutes." The division of families drove thousands of East Germans to plot their flight; hundreds of them died trying to escape. In 1989, the Soviet Union's grip on its satellite regimes weakened and a pro-democracy popular movement spread across Eastern Europe. The iron curtain crumbled, and East and West Berliners were allowed to meet. "It was a dream," says Rainer Hildebrandt, who in 1963 started Haus am Checkpoint Charlie, a museum which houses exhibits on escape attempts and the construction of the Wall. "It wasn't expected that it would go so quickly. And then, suddenly, people who didn't know each other fell into each other's arms." Traveling to Berlin 10 years after reunification, I find a resurrected city striving to meld its split personality. In acts of liberation, Berliners tore down all but a few small segments of the Wall, leaving behind a long stretch of open real estate in the city's heart. A business and leisure fantasyland dominated by DaimlerChrysler and Sony fills the void in Potsdamer Platz, an area that before World War II rivaled Times Square. In former East Berlin neighborhoods such as Mitte, which bordered the Wall, developers have restored and revamped dilapidated buildings that now house trendy boutiques, galleries, cafés, nightclubs, and lofts. I visit the Info Box, a temporary exhibition on Berlin's new development, and meet with manager Ariane Ribbeck. "Nowhere else in the world do you have a city like Berlin where you can build right in the center of town," Ribbeck says. "Berlin has a new city in the middle of the city, and this is because the Wall was here." Like most tourists who visit the city today, I want to see a remnant of what was once West Berlin's biggest attraction. In Mitte and Potsdamer Platz, people are selling pocket-size chunks of the Wall; two blocks from Potsdamer Platz, on Niederkirchnerstrasse, I run my hands along a graffiti-streaked slab of it. In the city outskirts, I track down more sizable traces. At Gedenkstätte Berliner Mauer, I talk to Hans Gissler who works in this small museum with exhibits about the section of wall that stands across the street. He tells me the remains are memorials to the victims, reminders of an irrational past, warnings to future generations, proof of independence. At the East Side Gallery, murals by more than 100 artists from around the world decorate the biggest remaining section (not quite a mile long). It's in the process of being restored and repainted because visitors—vandals?—secretly break off small chunks. They want a tangible token of liberty, and Berlin continues to be one of the few places where you can pack a piece of freedom in your suitcase and bring it home.

A bit pungent to be used in an official tourist brochure, perhaps, but as good a description of today's heady atmo- sphere as any. The concept of the Weltstadt, or world city, is particularly important to Berliners, who have never quite been sure their city deserved to be counted with Paris, London, and Rome. Now, they are beginning to believe.

"The heart is coming back," says Berlin Cityguide representative Gunter Friedenberg. "We are a capital again, and people see that they are part of what's happening."

For the visitor, what's happening starts in Potsdamer Platz. At one time it was the busiest square in Europe, the possessor of the continent's first traffic signal. But it was bombed into rubble in World War II and reduced to a weed-choked no-man's-land during the Cold War. As Paul Goldberger wrote in the New York Times Magazine, it was as if "Times Square had been replaced by a chunk of the New Jersey Meadowlands." Well, Times Square is back with a vengeance.

DaimlerChrysler, Sony, and several other corporations have poured billions into rebuilding the area, bringing in such renowned architects as Renzo Piano, Helmut Jahn, and Arata Isozaki to create a soaring monument to 21st-century capitalism. Jahn's Sony Center, with its vast futuristic dome hanging overhead like the spacecraft in Independence Day, draws a reported 50,000 to 100,000 visitors a day. Anyone who recalls the spot from just a few years ago must stagger out with an extreme case of cultural
vertigo.

For an antidote, head a few blocks east into Kreuzberg, the old radical quarter of West Berlin, which, though giving way in places to gentrification, still retains much of its seedy charm. Clubs such as SchwuZ and Tresor offer edgy attitude and driving techno well into the dawn. Once known as "Little Istanbul," Kreuzberg is still about one-third Turkish, and Turkish bakeries, groceries, and restaurants line the streets. There are any number of other good choices for dining, too. Altes Zollhaus, on the bank of the Landwehrkanal, serves gourmet German cuisine, while nearby Tres Kilos is, oddly enough, a Mexican restaurant. Cantina Trenta Sei, on a corner of Oranienplatz, and Sale e Tabacchi, a see-and-be-seen café, both feature terrific Italian fare.

While in Kreuzberg, be sure to visit the newly opened Jewish Museum, a jarring structure with a zig-zag design in titanium and steel that evokes a torn Star of David. Museum exhibits focus on Jewish history and art as well as the everyday lives of Jews in Berlin before the Holocaust.

Kreuzberg was also the locale of Checkpoint Charlie, the border crossing between East and West Berlin where in 1961 Soviet and American tanks faced off in one of the Cold War's critical showdowns. A reproduction of the guardhouse is there now, and there's a Checkpoint Charlie museum nearby.

On my way to visit Haus am Checkpoint Charlie, I experience a moment of almost cartoonlike symbolism. I am about to cross Friedrichstrasse at the corner of Kochstrasse to take a closer look at the sandbag-protected little hut when I hear the blast of a horn and jump back to the curb, just before a huge United Parcel Service truck goes barreling through the intersection without so much as slowing down. I watch as it disappears up Friedrichstrasse, past Gucci and Donna Karan shops, on its errand of commercial urgency and I think, "Welcome to the new Berlin."

Friedrichstrasse is indeed emblematic of the city's reinvention. The drab old concrete office and housing blocks of the GDR era have been demolished and replaced by a variety of new buildings. The lovely Galeries Lafayette, designed by Jean Nouvel, and the adjoining art deco-style Quartier 206, both below street level, offer upscale shopping and a food court that could keep me underground all day.

It is worth coming up, however, to visit nearby Gendarmenmarkt. Created in the 17th century, this lovely square, with its concert hall and two graceful churches, has been reconstructed since the war. A number of the city's finest restaurants surround it. Among them are the mosaic-bedecked Borchardt and Vau, a favorite haunt of celebrities and politicians.

If Gendarmenmarkt, with its haute cuisine, its chocolate shops (stop by Fassbender's on the square for a small box of truffles and a look at the 4-by-6-foot chocolate Reichstag in the window), and its quiet elegance begins to feel a little too, well, quiet and elegant, head north into Mitte. It is there, in the cafés, galleries, bars, and clubs of the Scheunenviertel, that Berlin's new pulse seems most vital.

Start by walking down Oranienburger Strasse, past the restored New Synagogue. Just down the block is Silberstein Café, a funky space in which all the chairs and tables are made from hunks of steel welded in exotic shapes and the visitor can get sushi and espresso at the bar as well as good wine by the glass.

At the end of Oranienburger Strasse is the Hackesche Höfe. This series of interconnected and architecturally surprising courtyards was restored in the 1990s. It now houses galleries, cafés, a theater, and a club called Oxymoron, which—fittingly, given its name—fills the graceful, turn-of-the-century space each evening with a pounding beat.

Next door to the Hackesche Höfe, in yet another Berlin face-off, is the Haus Schwarzenberg. This fiercely unrestored warren of alleys and courtyards has been transformed into an artists' collective. Here the Berlin air seems almost sulfurous.

Air of any kind is scarce inside Delicious Doughnuts, a low red box of a bar on the corner of Rosenthaler Strasse and August Strasse, which on my final night in Berlin is filled with young men and women dressed mostly in black and all, it seems, furiously smoking and shouting to be heard over the old rock and roll on the sound system. I am trying to carry on a conversation with a 28-year-old sculptor named Julien, who lives in Kreuzberg but whose studio is just around the corner. "Why," I yell, "do you live in Berlin?"

And just then, yes, the music stops.

"Because," says Julien, "there's always something new here."

If you're going . . .