It's Fès, not Fez. The latter is a hat of Turkish production, a dark red truncated cone with a tassel, not much favoured by the locals, despite what some guidebooks tell you. And Fassi is what the citizens of Morocco's fifth city call themselves. The confusion with the name is one of several misunderstandings about this astonishing place. Nineteenth-century orientalists, French expeditionary soldiers, drugged-up Americans of the Beat Generation (who enjoyed a cannabis jam known as majoun, taken internally) all knew Fès, but it has not secured a place in popular imagination in the same way as Marrakech.
Fès has not been smoothed to an undemanding sheen by waves of tourism crashing onto a grubby medieval treasure. No one has recruited the snake-charmers and water-sellers who satisfy the fairy-tale expectations of visitors to Marrakech's Djemma el Fna. It remains quite strange.
I told a huge, high-living, rambunctious, world-travelling Irish friend that I was off to Fès. He said with a slightly worried tone: "Ah. You do know it is very real?" I soon found out that he meant it is not nearly so pretty nor anywhere like as easy as Morocco's tourist officials would want it to be. Fès reveals its considerable charm slowly. On day one, you will perhaps find it charmless.
Access was always a problem: the erratic rail link from Tangier and Casablanca was an impediment to all but the intrepid, then British Airways failed to make a service from Gatwick work. Now a twice-weekly flight by Ryanair from Stansted gives us all the chance to be an explorer.
First surprise is on final descent, because you are astonished by the greenery: so far from being the yellow-brown desert scrub of imagination, Fès is in a vast, fertile plain of olives and vines shimmering between the Rif Mountains to the north and the Mid-Atlas to the south.
The airport itself is neat, tiny and slightly bemused by the arrival of an international flight, although a new terminal under construction suggests confident Fassi ambitions for tourism.
Further evidence of modernisation? From the Aéroport de Fès-Saiss it's a half-hour drive to the Unesco World Heritage Site that is the old city. You pass through the elegant, cool, white Art Deco nouvelle ville built by the French: all clean lines, boulevards, architectural fountains, international shops and black shiny Audis parked in the shade. You do not stop. Because the point of Fès is the medina, the old town which simmers behind 10 miles of heroic, crenellated, sun-tanned city walls. It was founded by the son of the Islamic saint who brought the faith from Iraq to the hitherto pagan and animist Berbers of the Maghreb. So successful was this religious import that by the Christian 12th century there were 785 mosques in the medina.
Today, as a millennium ago, there is no access for any sort of wheeled vehicle, other than a porter's trolley. Minus the porter's trolley, this is as it must have been in the days of Moulay Idriss. There are no straight paths and maps are unreliable. "Nowhere in Morocco does one recapture the spirit of the past more vividly than in Fès," the traveller Rupert Martin wrote in 1967. I would say that nowhere I have ever visited has given a stronger impression of what, in all its dirt, sweat, fumes, colour and bustle, a medieval city might have been.
This is not a city abandoned to the fey pleasures of frivolous European travellers. Instead, it teems and squirms: urgent but polite, and elegant while often rough. The souk combines filth and mystery with the medieval sense which only a sweating Satanic blacksmith in a carbonised vault and a man next door specialising in severed goats' hoofs can bring. Even lawyers sit in cubbyholes in the souk.
Architecturally, the souk is an intense psychological experience, but undistinguished aesthetically. The mosques are inaccessible to non-Muslims and the compromises of the plan mean filth underfoot is more of a diversion than explicit architectural delights. But your guide, and such a thing is necessary at first, explains: "You cannot tell a house by its door." And soon you find that, behind kicked, peeling and stained entrances sometimes stand imposing private houses with three-storey atriums, hypnotic tiling and overwhelming decoration.
The contrast with the out-of-town Jewish quarter, the mellah, is striking. Here, beyond the city walls, houses have balconies which address the world outside. Maybe there is a truth begging to be expressed here. Meanwhile, only an estimated 150 Jewish families remain.
Fès food is an anomaly. There is a weird mismatch between what's abundantly available in the souk and what appears on menus. The souk teems with sellers of herbs, spices, fried fish, lemons, escargots, goat, tripe and artichokes, but restaurant menus are repetitive. Boiled salads – including nerveless cauliflower – are served in miniature tagines they were evidently not cooked in. Insipid grey "chicken in sauce" appears everywhere. I looked in vain for harira (the ethnic soup) or méchoui (a whole cooked lamb) or any sense of freshness and precision in the cooking. Solemnly, our guide said, summoning-up unhappy memories of things ill-digested past: "In Fès, one does not eat fish." Still, smells memorably define the souk. Lemon verbena is an insistent presence, but so too is donkey.
We stayed in the Riad Maison Bleue. Literally eccentric, it is a conflation of three old houses haphazardly connected with central courtyards, dark spaces, precipitous tiled staircases and a roof terrace which, in full acknowledgement of the implied symbolism, places you between the noisy ring-road and the dark, smelly, traffic-free, souk. The staff were ethnic reminders of a history in which green-eyed Berbers, dark African slaves and Baghdadi Arabs have participated.
In the riad's hammam we had a voluptuous experience that sultans must have known. In stupefying steam, I was pummelled and scrubbed by a handsome woman. I was wearing nothing and this might have been disconcerting had it not been for my astonishment at exactly how much redundant skin she scrubbed away. In any case, my wife was on the slab next to me, covered in fragrant, gelatinous mud.
Other notable memories include a 90-minute drive to the hauntingly beautiful Roman ruins of Volubilis, capital of the old Mauretania, the empire's most south-westerly dominion. Nearby, is the city of Meknes, which bests Fès with a wall circuit of nearly 15 miles. The petite taxi (a disintegrating Fiat Uno) had a no-smoking notice and a headlining which had evidently been at some moment in the past torched in a dramatic blaze. As the muezzin began his midday cry, I found it was usually time for an excellent, cold Casablanca beer.
Always there is music half-heard through walls. And the lingering memory of wondering if I have ever felt more clean than after the hammam. We soon learnt that the medina is not as un-navigable as they say. After a day you can find your way and there are no risks, apart from the chance acquisition of a carpet.
But you have doubts. Why, when mint tea is so popular, has no one made a teapot which pours efficiently? Most times, the liquor escapes more readily from the loose-fitting lid than the congested spout. And what is the psychology of a modernising country which insists on making Berber slippers, camel saddles, leather accessories, djellabas and carpets which no one ever willingly buys?
Paul Bowles, spiritual leader of the American Beats, stayed at the Palais Jamai before the convention-goers with lanyards and gut-straining short-sleeved shirts arrived in what is now a Sofitel. He thought Fès "ten-times stranger and bigger and brighter" than his Moroccan base in Tangier. And he wrote to Gertrude Stein: "Fès is full of flies and dust, and rats knock everything over on the tables at night. It is quite dirty and very beautiful." And describing a visit to Fès in 1889, Pierre Loti commented on the "disdainful immobility" and "dusty rags" of the Fassi and added: "Sombre Morocco, long may you remain immured, imperturbable to novelty! Turn your back on Europe; abide motionless in times past! Long may your sleep continue; your ancient dream persist." There's not much reason to revise either assessment. Fès is not always pretty and it's often quite difficult. This is what my friend meant by "real".
I reflected on this atop my riad's terrace with a large glass of Celliers de Meknes syrah and a view of the kasbah. It was April and it was 30C. Real, I found, is a sometimes disconcerting, but generally good, experience.
The writer travelled with Ryanair (0871 246 0000; ryanair.com), which flies Stansted-Fès twice weekly from £51 one way; and with Lawrence of Morocco (020-7183 6401; lawrenceof morocco.com), which offers four nights at Riad Maison Bleue from £746 including flights, breakfast and transfers.
Eating and drinking there
L'Amandier, Palais Faraj, Derb Bensouda, Quartier Ziat (00 212 535 63 5356; palaisfaraj.com).
Al Mandar, Palais Jamai, Bab Guissa (00 212 535 634 331; sofitel.com).
La Maison Bleue, 2 Place de Batha (00 212 535 741 843; maisonbleue.com).
Riad Maison Bleue, 33 Derb Miter Talaa Kebira Ain Zliten (00 212 535 741 839).
Sammy has a reputation as the best guide and costs €40 per day (00 212 672 381 512).
Moroccan Tourism: visitmorocco.com
To see our 48 Hours film, visit bit.ly/Fes48