You see Chartres from miles away across the wheat. The Beauce is a vast, flat plain, one of the great granaries of France, and the cathedral rises out of it with two mismatched spires, like a ship on a green sea. After a fire in 1194 destroyed most of the earlier church, the townspeople rebuilt it in about thirty years, a remarkable pace for the time, and as a result the building has a unity that few Gothic cathedrals can claim. It was one of the first sites to be added to the UNESCO list, in 1979.
What really matters here is the glass. More than a hundred and fifty windows from the twelfth and thirteenth centuries survive, and the deep blue that glows in them, known as Chartres blue, has never been exactly matched. On a sunny morning, the nave fills with coloured light that moves slowly across the floor. Set into the floor of the nave is a stone labyrinth about thirteen metres across, which pilgrims once followed on their knees, and which is usually uncovered on Fridays during the warmer months.
The approach is pleasant riding. The roads across the Beauce are straight, quick and exposed to wind, with fields stretching to the horizon, and the lanes in the river valley of the Eure are gentler and greener. The old town below the cathedral is a tangle of steep, cobbled streets and half-timbered houses, best walked rather than ridden. Park outside the centre, where there are places for bikes, and go up on foot.
Chartres has about forty-four thousand people, so you will find fuel, supermarkets and plenty of cafes. The local speciality is the pâté de Chartres, a game pie, and the town has a long tradition of baking. The ride from here continues across the Gâtinais to Fontainebleau, a pleasant run through forest and farmland, and the whole day moves from a cathedral to a royal palace, a good lesson in French ambition. Go early and have the nave almost to yourself.