The mesmerising Bab Bou Jeloud, the “Big Blue Gate” of Fes, marks the start of its historic Medina, which is the world’s largest surviving medieval city. The side facing the modern city is decorated with striking blue zellij tiles, representing Fes’s specialisation in pottery and its discovery of the technique for producing such a bright blue glaze.

Once you walk past the gate, the sound of modern traffic fades away and is replaced by the hum of an ancient city, buzzing with thousands of voices, animals and footsteps, while concrete buildings morph into wooden stalls covered from the sun by a large piece of cloth. The difference between the Medina and the world outside it is so stark that it seems the gate separates not just two parts of a city but is a portal through time itself. Before you enjoy the sights and sounds of the Medina, turn around and look at the gate again. On this side, it is green – the colour of Islam.