Every great city is entirely itself and nowhere else. At the same time, they're all like ... somewhere. Somewhere that doesn't exist. A Platonic copy, perhaps; an embodiment of the idea of the city, whatever that may be. Morocco has several versions – all different – but in the end Tangier, Rabat and Marrakesh seem to me just rehearsals for the world's great masterpiece, Fez. In particular, the Bali Medina, the walled Old City, of Fez. The traditional Great City – traditional now, in our post-Enlightenment eyes – is a place of visual harmony, of vistas and prospects, squares, spires and domes. Old Fez is the exact opposite. The alleyways of the medina are so sinuous, straitened and overbuilt that there is, quite literally, no view. You never know what is around the next corner as it tilts down towards the river. You barely know where the next corner is. There is no angle that can lead the eye upwards more than 30ft. The rooflines are a mystery. The medina from the air reveals nothing about the medina on the ground. The eye is made useless.
Instead, you navigate by sound and smell. The clangour of hammers on metal leads you into a narrow defile, where brass-beaters and tinsmiths bang their trade. Here a vegetable steam announces the dyers, the streets robed in scarlet cloth hung to dry. A haunting, literally faecal, fleshy, fatty, ammoniacal smell declares that the great and terrifying Chouara Tannery is nearby – but where? Through what doorway, along which grease-skittered cobbles, up which narrow stairs?
Stay in one of the many riyads in Fez – built for extended families, now often converted into guest-houses where you can dine under the open sky, rooms opening on to balconies overlooking the central courtyards – and ignore the threats of getting irretrievably lost if you venture into the medina. Hire an official guide if you want; go alone if you don't mind your sleeve being plucked every few yards by boys eager for dirhams. Be prepared to be cheated; the oud-wood oil the perfumer offers you will be Firmenich Oud Synthetic 10760E or Black Agar Givco from Roure if you're lucky, a frantically dodgy concocted base (smelling of santalone, maple syrup and old gas-pipes) if you're not. It doesn't matter; you don't know what real oud smells like anyway and nor do your friends. The soft wool djellaba, naturally dyed, will be spun rayon, unnaturally dyed, and anyway you'll never learn to keep the hood pointed up, like a Klansman or a wizard. Bear with it. The medina is not about you.
It is about Al-Karaouine, the world's oldest functioning university (branched out from Qur'anic studies into geography and maths as a sort of competitive USP). The medressehs in every district. The scraps of silk thread on every narrow wall, left by the cord-weavers of the city with their little electric winding-motors. The tiny cubicles and low, narrow basement spaces where men ply unrecognisable trades. The donkey-shouts and sweetmeats and small doors which could lead into a finely restored riyad or a warren of hovels.
Get lost. That's part of it. Part of the quality of the great city: that you can become almost instantly, hauntingly lost. (The other part is that you can be easily found, that you can belong to it.) I can describe it for you if you are a perfumer: it is what Guerlain's Shalimar would be if there were no obscenity laws. I can describe it for you if you are an organist: imagine inhabiting the sound of the 17th-century Gabler organ at Weingarten Abbey. For the rest of us, all I can say is: if you abandoned a Brussels EU apparatchik in the medina, he would die of horror, screaming. In fact I can do better: Fez is the opposite of Brussels. Go there. It will populate your dreams.
# China's most dazzling city puts on a show: Shanghai World Expo (1 May-31 October) is expected to attract a record 70 million visitors. Better City, Better Life, is the theme. Packages including Expo tickets from Wendy Wu Tours (0844 875 2433; wendywutours.co.uk)
# Develop a taste for voluntourism in Vanuatu in the South Pacific. This holiday combines volunteering (renovations of houses and schools in a remote island community), with time to explore the volcanic island of Vanuatu. Hands Up Holidays (0207-193 1062; handsupholidays.com), 15 days from £1,450 pp.
# Explore India's Western Ghats and the Prambimulum Wildlife Sanctuary, one of the world's 34 bio-diversity hotspots and home to endemic species like the Royal Bengal Tiger. TransIndus (020-8566 2729; transindus.com) has three-day tented camp excursions from £498 per person.
# Take an exotic cookery course in Vietnam with Holiday on the Menu (08708 998844; holidayonthemenu.com). Learn different regional dishes and take a chef-guided market trip, with accommodation at the plush Life Resort in the UNESCO port town of Hoi An. Seven nights from £799 per person.
# This new Japanese riverside "hoshinoya" (upscale traditional inn) Hoshinoya Karuizawa (hoshinoya.com/en) is a forest-cloaked eco-retreat with natural hot springs and meditation bath. Doubles from £94 per night.Reuse content