Living with the dark and brooding presence that haunts heart of Europe's loveliest city

I was attracted to the restaurant by the name, Mucha, and the Art Nouveau posters that adorned the entrance hall. Pastoral images of girls with flowing hair and limp gowns like nighties, images that are used to market such French products as cognac and perfume.

But why here, why in Prague? Mucha was one of Europe's great Art Nouveau illustrators. He studied in Munich and Paris, designed costumes for Sarah Bernhardt, prospered under the patronage of a Chicago industrialist and - those posters again - created advertising images that are locked in one's mind as quintessentially French.

The surprise, of course, was that Mucha was Czech. It was a small surprise in a city full of them, the biggest surprise being the city itself. It is stunningly beautiful, beautiful beyond expectation. Better-travelled friends said it was so, but nothing quite prepares you for the scale of the place: the centre of Prague is an architectural gem, embracing several square miles of unspoilt streets and narrow winding alleyways that adhere still to their original medieval pattern.

They twist and weave higgledypiggledy, running over cobblestones and down steps. Around a corner, they might branch out into something wider, lined with shops (many selling puppets or wooden toys or glass), or balloon into a square crammed with people, tourists and hawkers.

The red-tiled rooftops run their own riot across the top of the city, peppered with skylights and elevations at every angle. There is a fairy-tale feel to the place. And as you wander the streets exploring, music wafts through the air. Mozart mostly. They waste no time telling you that Don Giovanni had its premiere here in 1787, and the Czechs have been coining it ever since (they seem less proud of their own man, Dvorak, for some reason).

Don Giovanni pops up regularly over the entrances to pubs and restaurants, but for all the commercialisation they are into the real thing, too. You can hear a superb Requiem for about a fiver in the magnificent Rudolfinum concert hall, or any number of classical pieces in churches and halls in the centre of the city.

There is more than 1,000 years of architectural heritage here (as my guidebook, Time Out Prague, helpfully explains), Romanesque, Gothic, Renaissance, Baroque, revivalist and Art Nouveau. And it is all so astonishingly well preserved: by some extraordinary stroke of good luck, the ravages of the last war seem to have passed Prague by.

Back to Mucha and lunch. Pork, wild boar, a sweet gravy and dumplings. (Dumplings with everything. If you do not like dumplings, avoid Prague. In fact, if you don't like meat, life will be difficult. It's not so much a case of meat and two veg, as meat and two meats. And dumplings.)

At the next table there sat two men. One old, perhaps well into his 80s; the other younger, perhaps in his early 70s. The younger man was leading the conversation, in fact he was totally dominating it. He spoke in English, with a distinct English accent. The older man said little, but what he did was said with a heavy Czech accent. Both were Jewish.

The younger man explained his life in opera. He had worked in Sydney and London and Paris. He was full of advice for the older man, advice as to how the Czech Republic should develop, how Prague's traffic problem might be solved (not much of a problem to my Dublin eyes; trams rule the streets) and how the Czech language might fight back against English. (He had written a long letter to President Havel on this point and was miffed at the absence of a reply.)

Most of all, however, he wanted to hear from the older man about his, the younger man's, plans that the Jewish youth of Prague should be taught their history.

The Jews of Prague were among the oldest of east Europe's Jewish communities, having been in the city for at least 1,000 years. Yet in the space of just a few years they were wiped out, almost totally. The old man in the restaurant was a rarity, and there aren't many young Jews either.

During the war some 300,000 Czechs lost their lives, and most of them were Jews. In the centre of Prague, in the area called Josefov, the Jews lived in their ghetto for most of 1,000 years. After they left the ghetto in the late 18th century and spread themselves more evenly throughout the city, they dominated its cultural life, producing the likes of Franz Kafka, and enriching Czech life immeasurably.

Ninety per cent of the Jews who remained in Prague at the outbreak of war were murdered by the Nazis. In one instance 140,000 were herded into the Theresienstadt ghetto north of the city. A model community, said the Nazis, of happy Jews simply living apart from the rest of Czech society.

The Red Cross came, looked and was impressed. It told the world that the Czech Jews were safe. When the Red Cross left, the Jews were all taken to Auschwitz.

But the buildings survived in the main. As Time Out puts it, "the only thing that saved some Prague's synagogues and communal Jewish buildings from the Nazis' routine destruction was the Germans' intention to use them after the war to house `exotic exhibits of an extinct race' ".

Josefov forms a large part of the architectural jewel that is the centre of Prague today. But the city centre has one characteristic that I have not mentioned: there is something dark and brooding, menacing almost, about the place.

You get it walking across the Charles Bridge in the evening, crossing the river to visit the Castle. The statues that line the bridge, laden with crosses and silhouetted black against the sky, seem to stand like silent Gothic judges.

I expect it predates the genocide committed against the Jews, but laced through this pretty fairy-tale city crammed with young people in the summer sunshine there is a distinct feeling of evil somewhere.

The younger Jewish man, the English opera buff, wanted to make a donation to some body or other to promote the teaching of the history of Prague's Jews. The older man, looking tired, listened but affected no great interest.

His view? The old Jew of Prague said nothing. He kept his memories to himself.