Then add billowing, Wagnerian harmonies, minimal melodies, solemn electronic mantras.For psychedelic and Goa trance, the mixture is spiced up with bleeps, squelches, roars and other weird effects. None of which could be said, of course, of any conventional nightclub you care to mention.Musically speaking, the basic recipe has remained fairly constant (stagnant, its detractors would say). Take a fast four-four beat, add synthesised snare drums and sizzling high-hat. Underpin the rhythm with a rumbling, echoey bass and something softly pulsing in the middle. Drinking-water is free, children are welcome, and alcohol is conspicuous by its absence. Unlike most of the other dance trends of the Nineties, which quickly embraced the profit motive with open arms, purist trance has always retained a determinedly anti-commercial stance Most trance events still don't charge for entrance.

But in the late Nineties there was a sudden creative lull in the dance-music industry, which looked around for something to fill the gap; 1998 was promptly christened the year of trance, making chart hits out of trance-inspired tracks such as Greece 2000's "Three Drives on a Vinyl", and stars out of DJs such as Ferry Corsten and Paul van Dyk (a Dutchman and a German respectively).Clubs such as Gatecrasher in Sheffield, pioneers of the new streamlined trance sound, were thronged with teenagers for whom acid house was something their parents danced to, waving fluorescent light-sticks and guzzling Ecstasy by the handful.The underground trance scene looked on all these developments with mixed feelings. Mainly from the latter, it soon picked up a New Age, mystical dimension that distinguishes it from the harder-edged, more urban sound of techno.For a long time trance was underground music, played at free parties in the countryside and at occasional club nights such as London's Escape from Samsara and Return to the Source. It first emerged in Europe during the early Nineties, fruit of a strange marriage between German obsessions with Kraftwerk and Seventies progressive rock and the twiddly psychedelic music played at the full-moon parties in Goa (hence "Goa trance", now merely one of the genre's multiple variants). Its origins are not well understood, though essentially it seems to be a child of acid house and a second cousin of techno. Sample: "Trance seeks to lift you right out of your body, out of your head, out of your mind, right out of the dimension you are currently occupying." And: "It takes out your soul and makes your head explode into a million pieces."For a student of the Byzantine complications of Nineties dance music history, trance presents an intriguing conundrum.

Trance music and attitudes are making converts in countries as little associated with a vibrant youth culture as Mexico, Russia and Israel (now one of the heartlands of the trance scene).A casual surf through the murkier waters of the Web (trance and the Net were made for each other) brings forth a deluge of sites, many of them given over to rambling paeans of mystical rapture through dance. Love it or hate it, it is in fact the first truly global pop music, leaping boundaries of culture, race and language with athletic ease. That is hardly surprising when you consider that this form of electronic dance music lacks most of the traditional attributes of pop music, including lyrics, voices, instruments, verse-chorus structure and artists you might recognise as such.But whatever anyone's opinion of it, trance is not going away. On the beaches of Thailand it was hard to get away from the pounding music and writhing bodies, moaned one traveller who went in search of peace and quiet.Most sensible people have little time for trance Music critics almost universally loathe it. On the top of a cliff in Ibiza, the dawn of the century kicked off a three-day party attracting the island's entire alternative community.There were raves in Bali, Brazil, New York and New Zealand - not to mention in Disco Valley, in Goa, the spiritual home of trance music and the cyber-hippie lifestyle that surrounds it.