Fez is Morocco's spiritual and intellectual capital, and the most rewarding city in the country to lose yourself in. The walled medina of Fes el-Bali is the largest car-free urban area on earth — nine thousand alleys, dead ends, fondouks and squares packed into a bowl in the Saiss plain. The whole old city is a UNESCO World Heritage site and it has changed remarkably little since it was laid out in the ninth century.
There are really three towns. Fes el-Bali is the medieval medina, founded in 789 and built up by waves of Andalusian, Tunisian and Berber immigrants. Fes el-Jdid ("New Fez") is the comparatively young royal quarter, walled off by the Merinid sultans in the thirteenth century, with the Mellah (the old Jewish quarter) and the Royal Palace. Ville Nouvelle is the French-built grid to the south-west, where most of the modern hotels, restaurants and bars are.
The headline sights are inside the medina. The Al-Qarawiyyin mosque and university — founded in 859 by a Tunisian woman, Fatima al-Fihri — is generally cited as the oldest continuously operating university in the world. Non-Muslims can't enter, but you can peek in through the gates and visit the attached library after restoration. The Bou Inania madrasa is the masterpiece of Merinid architecture, all carved cedar and zellige tilework, and one of the few religious buildings in Morocco that is open to non-Muslims. The Chouara tannery, viewed from the leather-shop terraces above, is the postcard image of Fez: men working dye pits in primary colours that have not changed since the Middle Ages. Take a sprig of mint for the smell.
Stay in a riad — a restored old townhouse around a central courtyard — inside the medina. They are everywhere, vary wildly in price, and are the right way to experience the city. Hire a guide for the first day; the medina genuinely is a labyrinth and a guide will take you through workshops you would never find on your own. After that you should get lost on purpose. The general rule: walking downhill takes you towards the centre and the river, walking uphill takes you out.
Fez is less polished than Marrakesh and harder going for first-time visitors — touts can be relentless, the medina is exhausting, and good restaurants are mostly hidden behind blank doors. Stick with it. Three days is a minimum; a week is better.