THERE comes a moment in the life of every traveller when a terrible realisation strikes: there are only so many journeys left. The youthful notion that a lifetime is more than enough to see a whole world is replaced by the sense that your income and your holiday entitlements are going to keep you at home for most of every year.

And that could mean you're looking forward to only 20 more voyages of discovery before you become too creaky to climb on a plane, boat or train. From this point on, you must make every journey count. So you start to reflect on why you go travelling at all. If your answer is "for the scenery", you'd better click on another page right now, because that is not my answer. I reckon we travel to understand the world, and ultimately ourselves.

The unexamined journey is not worth making. If reality imposes a limit on the time we can spend travelling, then we should be heading only for the places that will stimulate our imaginations.

For me, that means where the world's biggest ideas were born — where somebody decided that the earth revolves around the sun, or that humans are descended from jellyfish, or that office blocks can be beautiful, or that communism works best when served with good food. These are the places that make your spine tingle as you stand in them, because you know something happened here that transformed the planet.

The Hindus use the word darshana for the mysterious ecstasy generated in the presence of a holy place. Modern western travellers may experience darshana under more secular conditions. The first time I felt it was in the flat of Sigmund Freud, in Vienna, when I realised that this room produced the most influential theory of the 20th century — that human behaviour is largely driven by the unconscious mind. The second time I felt darshana was inside El Transito synagogue, in Toledo, Spain, when I realised that 600 years ago, Muslims, Arabs and Christians gathered in this space to share their scientific discoveries in a triumph of human collaboration that has never been repeated.

I decided that from then on, I would travel in search of darshana, getting my ecstasy fixes in the places that generated this century's dominant imagery.

And if I could enjoy a couple of great meals, relaxing swims and even the odd view in the process, so much the better. You are reading a progress report on a lifetime project.

The Hindus have another word, pradakshina, for the ritual of walking around a holy place and meditating on what it means. Using a broad definition of the word holy, I hope this book will help readers to engage in that ritual. I toyed with the idea of calling the book Pradakshina, but I didn't want to risk confusion with Shirley Maclaine's next autobiography.

So I decided to name it for its content - the places that are essential for anyone who is excited by the world of ideas, the places that every thoughtful stay-at-home needs to know about and every passionate traveller needs to visit. The destinations appear in alphabetical order, but it's not necessary to read the book that way. Many themes weave through the chapters, linking places, people, myths and theories in ways I hadn't even realised until I was well advanced in the writing.

Sigmund Freud probably shared a table with Adolf Hitler in a Viennese cafe. Freud was obsessed with Tutankhamun's father. Charles Darwin wrote to Karl Marx. Vincent van Gogh painted the hills from which Nostradamus studied the stars. Albert Einstein wrote the theory of relativity in Prague and Zurich, but the manuscript ended up in Jerusalem. Woody Allen stayed in Cesar Ritz's mansion in Paris. Frank Lloyd Wright designed the Blade Runner's apartment in Los Angeles. So you could treat this book as a collection of journeys through a landscape of ideas, and navigate in accordance with your particular interests. Here are some themes you could follow:

The political journey. This might begin in chapter 4 with the Tolpuddle Martyrs, who discover trade unionism and are sent to Australia for their trouble. Also in chapter 4, Karl Marx invents communism, but doesn't live to see its energising effect on Union Square, New York (21), or its success in Bologna (2), or its collapse in Prague (16). Meanwhile nationalism inspires the Nazi takeover of Vienna (5), and the push for California to secede from the United States (24). And in chapter 26, Switzerland emerges as a model of political perfection.

The religious pilgrimage. This might begin in chapter 22 when Tutankhamun's father decides that the world is run by one god rather than many. His monotheism doesn't stick, but a thousand years later the Jews take the ball and run with it through chapter 10, where they are joined by the Christians and the Muslims. The Jews and Muslims come up against the Spanish Inquisition in chapter 20, while Martin Luther starts reforming Christianity in chapter 2.

The artistic journey. Vincent van Gogh finds his colours in chapter 1; Tutankhamun inspires the Nile Style in chapter 22; Louis Sullivan turns skyscrapers into temples and Frank Lloyd Wright designs suburbia in chapter 3; Andy Warhol sets up his Factory on Union Square (21); while Queensland just thinks BIG is beautiful (14); Cesar Ritz perfects the art of hospitality (18); and a museum which walks the line between art and madness thrives in Switzerland (26).

The scientific investigation. Archimedes uses physics and geometry to defend Syracuse in chapter 19; Copernicus and Galileo turn the universe around in chapter 2; Darwin turns humanity around in chapter 4; and the spirit of Einstein finds
rest in Jerusalem (10).

The psychoanalytic journey (or the Head Trip). Freud unearths the unconscious mind in chapter 6, Jung extends it into a theory of myths and archetypes in chapter 26, and Hollywood uses Jung to create the formula for a successful movie in chapter 8. Meanwhile, Jerusalem turns out to be a mental health hazard (10).

The sensual exploration. You might follow your nose to the perfume capital of the world in chapter 7, and to the source of the world's most expensive wine in chapter 25. The cultural importance of food fills chapter 5 and reinforces Indian tribal identity in 17; Australia's gastronomic heart proves to be in Noosa (14); and the political role of the palate becomes apparent in Bologna (2).

The musical progression. Venice celebrates Vivaldi's Four Seasons in chapter 23; Smetana composes a river where Mozart met Casanova in chapter 16; Don Maclean sings about Vincent (1) and Steve Martin sings about King Tut (22); there's a shrine to Elvis Presley in Miami (13); and Nellie Melba inspires a pudding in London (18).

The literary journey. Mark Twain tours the Holy Land in chapter 10; Jane Austen and John Fowles haunt Lyme Regis (4); James Joyce passes Lenin in Zurich (26); Carl Hiassen and James Hall revel in Miami's crime (13); Vaclav Havel has to give up playwriting for politics (16); and William Randolph Hearst sells papers and buys Europe to build Xanadu (24).

Of course, you may simply be looking for a guidebook which describes the most interesting places to visit in a particular country. Then you could deconstruct Essential Places nation by nation ...

France. You'll find Provence in chapters 1 and 23; Paris in chapters 5 (the restaurants), 18 (the best hotel) and 23 (the bridges); Grasse in 7; and Bordeaux in 25.
Italy. You'll find Bologna in chapter 2, Rome and Florence in 5; Venice in 5, 18 and 23; Capri in 9; Orvieto, Assisi and Gubbio in 15; Sicily in 19.
The USA. Chicago is in chapter 3; the food of New York, LA and Seattle is in 5; Hollywood is 8; Miami is 13; New York is 21; and California is 24.
England. Darwin's home, called Down House, is spelt differently from the neighbouring village of Downe and is in chapter 4; so is Dorset; London's food is in 5.
China. Hong Kong's food is in chapter 5, belief system is in 11, and best hotel is in 18.
Austria. Vienna is in chapter 6, its alleged river is in 23, and its food is in 5.
Greece. The island of Hydra is in chapter 9.
Vanuatu. Port Vila and Erakor are in chapter 9.
Israel. Chapter 10 covers Jerusalem.
Switzerland. Chapter 12 is a journey down the Swiss spine from Zurich through Lucerne to Locarno; Lausanne's food is in 5 and its best hotel is in 18; and Zurich is 26.
Australia. The Sunshine Coast of Queensland is in chapter 14.
Spain. Toledo is in chapter 20. The foods of Madrid and Segovia are in 5.
Egypt. Luxor is in chapter 22. Cairo's food is in 5 and its river is in 23.
If jumping around like this sounds too complicated, start at chapter 1 and read on. The patterns will become apparent.

There are 26 chapters in this book, but they contain reasons to be curious about some 35 destinations. Of course I am not claiming that these are the only essential places in the world. They happen to be 35 I have reached in 24 years of travelling. My next 30 years will be devoted to finding the others. If you know of any places which are essential because of what happened there — places that inspire darshana — please write and tell me about them: ddale@essentialideas.info.
My list grows longer every day.

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