All backpackers worth their salt know what it is to sleep in smoky Bombay dormitories with self-righteously dirty Austrians and Germans, who suddenly whip crafted pipes out of their clothing just at the moment your eyes were about to close in sleep.
The elaborate lighting-up ceremonies, the smoky suckings and puffings, the silent offering around of the pipe like a sacred talisman; these rituals mean as much for travel as Delhi belly and the InterRail card.
And look at those generations of students riding the waves to Holland every Christmas vacation. As we all know, ragged young intellectuals do not cross the North Sea for tulips or the Van Gogh Museum. They go for dingy peace cafes where spliffs appear on the menu next to the mushroom quiche.
In years gone by, the further you travelled the further the view disappeared into aromatic smoke. Before the war the place to smoke a pipe was China. Shanghai was so sinful that a blast of opium before bed was as respectable as a glass of sherry.
In the Fifties it was Saigon and Hong Kong that filled with travelling dope-smokers, while the Sixties saw dope shops spring up on the road to Goa like garrison cities on the Silk Road. Istanbul's famous Pudding Shop was where you stocked up on the stuff before taking the long dope road to India and Nepal. And if you couldn't make it to Katmandhu you took the short cut to Marrakesh instead.
Otherwise you went to countries where the whole local culture revolved around "substances". Countries such as Columbia where a mouthful of coca leaves was the local equivalent to a mid-morning coffee, or the Yemen where cabinet ministers chewed qat to discuss the national budget.
Meanwhile, airports from New York to Singapore crunched to the sound of dope being walked on, hidden inside travellers' shoes, while rucksacks swilled with cannabis fragments disguised as bits of dirt. Personally I call it madness, but there is no end to the madness of people who associate dope with travel.
And yet how things have changed. Smoking dope in Tony Blair's Britain seems such a tame affair compared to the same, heart-stoppingly dangerous offence in, say, King Hassan's Morocco or Lee Kwan Yew's Singapore.
It won't be long before long-haired dropouts from the universities of Delhi and Bombay start making pilgrimmages to British seaside resorts, where they will play didgereedoos and relax naked under the stars. The curious residents of Bournemouth and Brighton will earn pocket money by selling dope to naked junkies.
Still later, in a long overdue act of retribution, the Chinese will send their gunboats and force us to buy dope by the tonne, whether we like it or not. We will no longer need to travel for our dope and the tides of cultural history will have changed yet again.