I am writing this on Büyükada, one of the Princes Islands in the Sea of Marmara. The American writer friend who introduced me to the island claimed once to have had sex with six Kurds here. They were workmen, apparently, who were restoring one of the beautiful old wooden houses (yalis) with which the island is covered. He was passing, he caught their eye, or they caught his, and the rest is history.

Gays have a secret language to which heterosexuals appear not to be privy. We were walking down the hill to dinner when we passed the yali in question. He pointed it out, first drawing my attention to the elaborate fretwork carving of the balcony, then he told me about the Kurds with their beautiful blue eyes. I said, "Six? What, all at once?" "No, of course not, silly. One after the other."

I have never had sex on Büyükada. I've never even come near it, unless the charming hotel manager coming to meet me off the late boat from Bostanci because he thought I shouldn't walk the 200 yards to the hotel alone counts as anything more than gallantry. Yet Büyükada is one of the most romantic places in the world.

There are no cars here (except for a garbage truck and one, or maybe two, police vans). You go everywhere by horse-drawn carriage - a surrey with a fringe on top, like the one immortalised by the song in Oklahoma - drawn by pairs of matched bays or greys. The only sounds you hear are the clip of the horses' hooves; the clinking of the reins; the querulous-teething-baby cries of the seagulls; the strangulated screams of the fighting or mating cats (these two are often indistinguishable); and the fog-horn call of boats arriving and departing all day long from dawn until midnight. All you smell is sea and jasmine and grilling meat and fish.

If you look across the Sea of Marmara, on a clear day, you can see the angular silhouettes of Bostanci, Maltepe and Kartal, those densely-populated, intensively built-up outer suburbs of Istanbul; they look like a larger, less elegant Manhat tan, and seem alarmingly near. I prefer it when it's hazy, like today, and the Asian shore looks far away. There's a point at dusk, before the million lights on the far coast are turned on, when the sea and sky merge to become one, and there's just a wall of grey-blue.

But enough of Büyükada - whose erotic potential I am clearly not destined to experience (at least, not on this trip). That's the whole point. You can't plan your erotic travel. If you do, you're just a sexual tourist and that's not the same thing at all. Travellers are looking for adventure, and some are prepared to be more adventurous than others. "Relief", or titillation for his jaded palate, is the aim of the sexual tourist.

What is it exactly about sex and travel? The one enhances the other. Both involve exploration and experimentation; linking the two is almost irresistible. A romantic and unusual, preferably exotic, setting compounds the thrill. The more exotic the setting, the greater the kick. It doesn't need to be about danger, though some travellers clearly find an element of risk a turn-on.

In 1980, the Anglophile American scholar Paul Fussell published a book called Abroad. The book contained a chapter entitled L'Amour du Voyage, in which Fussell claimed that "Making love in a novel environment, free from the censorship and inhibitions of the familiar, is one of the headiest experiences travel promises."

The operative word here is "promises". The traveller, like the sexual adventurer (of whom some homosexuals seem to be the most daring - although some might think "reckless" a better word), embarks on his quest in the hope of encountering the unknown. Erotic travellers are, as the old song would have it, "Strangers in the night exchanging glances/Wondering in the night what were the chances/We'd be sharing love before the night was through." For these lovers at first sight, love (and sexual adventure) is simultaneously just a glance away and many miles from home. The promise of a foreign affair, that enticing combination of the erotic and the exotic, can prove unbearably alluring.

The trailer that advertises the video of the film version of Han Suyin's novel Love is a Many-Splendoured Thing promises that "Passion loses control in exotic Hong Kong". Implicit is the suggestion that uncontrollable passion and sexual adventure (even, with luck, depravity) beyond wildest imaginings, are possible only in such places as "exotic Hong Kong". But, in EM Forster's story The Obelisk, written in 1939, the travel undertaken by a schoolmaster and his wife is merely to an out-of-season seaside resort. Nonetheless, it leads to a chance encounter with two sailors, which in turn leads to sex, which leads to unprecedented perception, none of which would have been possible if the couple had not "travelled".

I've enjoyed my share of love-making in exotic spots and understand all too well the relationship between the place, the moment, the situation and the person, which all combine mysteriously to create an atmosphere ripe for adventure.

There's something magical about tropical countries: the strangeness, the dreamy warmth, the scent, the fact that no one in the real world knows where you are or what you are doing. In the right circumstances, that most depressing of encounters, the one-night stand, can seem positively thrilling. As the old poem has it, "Wouldn't you like to sin/On a tiger skin/With Elinor Glyn?" The tiger skin is the real attraction.

I have always found the east - I suppose I might as well go all the way and call it the Orient - particularly evocative. I first understood its erotic potential in Canton, in a Ferris wheel that revolved slowly high above the city. Later that evening, back at a hotel on the banks of the Pearl River (the name alone evokes a kind of magic) with the sounds of the boatmen in their sampans on the water, all scruples were forgotten, all cares banished; London, other obligations, other people, everything ceased to exist. Only the moment remained. You can recognise such moments, not just afterwards when they linger in your memory with a crystalline clarity, but at the time, almost as if you have taken a drug that intensifies your senses - of smell, of sight, of hearing.

My experience in China was followed by others - to the extent that I came to associate the Far East with a particular kind of erotic experience - and, when I was back in England with its monochrome colours and its gloomy climate, I would take out and examine my store of such memories rather as a miser might gloat over a secret hoard. The second time was on the Star Ferry pier in Hong Kong; the third in Raffles Hotel in Singapore. Raffles, in its last, great, seedy days before it was refurbished and lost all its character, was a real turn-on.

I had just arrived from London. When I got to my hotel, a gleaming, modern skyscraper, I found a message telling me that an old boyfriend happened also to be in Singapore and was staying at Raffles. I caught a cab and went over. We had one drink, then another, and then dinner. Just as I was almost fainting with exhaustion, saying, "I really must get some sleep," he said, "Come and have a look at the Tiffin Room."

The Tiffin Room, as far as I can remember, was a monument to colonial glory, festooned with stuffed tigers' heads and glass showcases containing reports of sporting triumphs. So, when he kissed me and said, "Come upstairs for a bit," I thought: "Well, why not? How often does opportunity knock in Raffles?"

S ome years later, I found myself in Siem Reap, in the Grand Hotel d'Angkor when it was still shabby and atmospheric before the Raffles group (which now controls almost all the great hotels in the east) got their hands on it and renovated the life out of it. I went to bed with a handsome mine-clearer who was risking his life on a daily basis helping clear the mines scattered like handfuls of rice by the Khmer Rouge.

We had stayed up late, drinking whisky and listening to the time-warp sounds of the Doors with a group of UN soldiers and whatever women their sergeant had been able to round up. When the party showed signs of getting out of hand, he asked if he could come upstairs to collect the copy of Conrad's Victory I had promised to let him have. I did give him the book, but that wasn't what he had meant. I had breakfast with him the next morning but, after that, I never saw him again. It didn't matter a bit. The evening and the night that had followed had been, in their own way, quite perfect.

In the early 90s, when my travels ceased to take me east, I discovered that it was possible to enjoy myself in Martinique, Guadeloupe, St Vincent, Grenada, New York, Paris, Venice, Seville, on the night train to St Petersburg...

• Erogenous Zones: An Anthology of Sex Abroad, edited and with an introduction by Lucretia Stewart, is published by Random House/ Modern Library at £14.99.