The World Heritage Committee recently inscribed Sidi Bou Said on the UNESCO list - and not for a temple or a palace, but for a colour. Two colours exactly: whitewashed wall and cobalt blue on every door, grille and window.

The village is scattered across the hill of the mountain with the lighthouse, twenty kilometres from the Tunisian capital, looking straight out at a sea that glows below with an improbably intense blue. And there is the first problem with Sidi Bou Said: because it is so close, most people come for three hours and go back. That is a mistake.

One British baron and one decree from 1915

To understand how the most photographed village in Tunisia came about, you have to go back to the twelfth century, when Abu Said al-Baji, a scholar and Sufi mystic, founded a shrine on the hill. But the form that fascinates today has a different author, and a modern one.

Rodolphe d'Erlanger, a British baron, painter and musicologist, arrived in 1912, fell in love with the place and pushed through a decree in 1915 ordering "all facades to be whitewashed", restricting the colour of doors, grilles and windows to cobalt blue. So the aesthetic for which UNESCO now protects the village is the result of a foreigner prescribing how the locals would live.

Sidi Bou Said had some protection from 1979, but only as part of the Carthage archaeological site. Now it gains its own standing - for architecture with an al-Andalus inheritance and for historical significance as a centre of spirituality in the Mediterranean.

How to get there, and more importantly - when

The cheapest and most authentic way is the TGM suburban train, which cuts across the Lake of Tunis and drops passengers below the hill in about thirty-five minutes. The classic yellow taxis do it in twenty-five.

The practical advice is singular: early morning. From mid-morning the main street fills with guided groups. Whoever arrives early gets the light bouncing off the whitewashed walls, without having to walk around tourists.

The cemetery nobody writes about

The least visited and most powerful corner of Sidi Bou Said is not a cafe at all. The cemetery spills down the rock in terraces, looking straight into the Gulf of Tunis. The graves are blindingly white, many of them nameless, scattered across the hill among prickly pears, aloe and bougainvillea. Silence, and one of the cleanest Mediterranean panoramas you can find.

Art behind the facades

The village inspired creators such as Paul Klee and Simone de Beauvoir, and to this day sustains a serious art scene. Ennejma Ezzahra palace is a compulsory visit, the former residence of Baron d'Erlanger and today a centre for Arab and Mediterranean music - inside there are wooden ceilings, plaster ornamentation and gardens hanging over the rock.

Dar El Annabi is a large eighteenth-century bourgeois house with an Andalusian courtyard, traditional wooden window grilles and a roof terrace looking onto the minaret. The Aicha Gorgi gallery, meanwhile, shows contemporary Tunisian artists.

Where to eat and where to stay

Dar Zarrouk, near the marina, has a courtyard under mulberry trees and a glazed terrace where you eat fresh fish, brik with egg and tuna, or couscous. Au Bon Vieux Temps is the other classic, with a terrace under vines and a menu mixing French and Maghrebi cooking.

The real privilege, though, is staying once the sun sets and the buses leave. Dar Said is a hotel in a nineteenth-century bourgeois residence with only twenty-four rooms around courtyards full of jasmine. La Villa Bleue stands above the rock, with hand-painted ceilings and a small spa.

The ritual you do not skip

Cafe des Nattes on the square is a legend - an interior clad in ceramic, a floor covered in rush mats, and mint green tea served very sweet and crowded with toasted pine nuts. If you head down through the alleys, Cafe des Delices has the definitive panorama of the gulf from cascading terraces.

And before heading back - bambalouni from a street stall, soft thrown dough dusted with sugar. That is the end of a day in a village UNESCO decided to preserve forever, because one man a hundred and eleven years ago decided what colour the doors would be.