Long shadows tapered into the darkening evening. Archways lengthened. Towers grew taller. Lit up at dusk, the citadel of Carcassonne looked spectacular, the illuminations adding an eerie quality that set my imagination racing. As I walked along a cobbled passage, I glimpsed the edge of a troubadour's cape disappearing around a corner ahead of me. I caught up with a cat several paces later.
It was for such impact and chimera that I was following a trail around the fortress city at nightfall. I was on a self-guided walk devised by the author Kate Mosse and set out at the end of her best-selling novel Labyrinth. For those not familiar with this page-turner of an adventure book, the story revolves around an ancient grail and is set simultaneously in the present and the 13th century, when Carcassonne and the land of the Occitan people were subject to a brutal papal crusade. Known as the Albigensian Crusade, this was a war the Catholic Church waged on the peaceable (and Christian) Cathar sect along with its sympathisers and aristocratic protectors. Last October Carcassonne buzzed with actors and camera crew filming an adaptation of the book: the two-part series starring Jessica Brown Findlay and John Hurt will be shown on Channel 4 next weekend.
History and make-believe: the novel and mini-series have a neat resonance, for Carcassonne's iconic citadel is itself partly a work of architectural fiction. It's a fabulous fantasy of a place: two rings of whopping, crenellated walls are punctuated with watchtowers that might have been magicked there from the pages of a fairy tale.
Known as La Cité, the citadel was famously rescued from near dereliction in the 19th century by the Gothic Revival architect Eugène Viollet-le-Duc. He redevised the tops of the walls and the towers and turrets (all 52 of them) but was much criticised for using what was considered the wrong kind of stone, and he added elements such as cone-shaped roofs that were deemed inauthentic. The overall effect, though, is terrific.
You see some of the most obvious 19th-century additions in the southern area of the walls, as Kate Mosse points out in her Labyrinth Walk. Following the writer's guide I snaked along winding alleys taking in the façade of the Basilica of Saints Nazaire and Celse – its gargoyles, reconfigured in the 19th century, looked particularly ghoulish in the night lights. I paused by the entrance to La Cité's amphitheatre, a modern addition where pageants are staged in summer; I stopped at café-fringed Place Marcou then wound my way past Chateau Comtal where the Trencavel family, viscounts of Carcassonne as well as Béziers and Albi, lived with their great entourages; I passed the big well still standing at Place du Grand Puits and walked between the two rings of walls, where knights once jousted, to grand Porte Narbonne, the main gateway to the citadel.
On my evening walk it was too late to go into any buildings in La Cité, so the next day my first stop was the basilica. Once containing a finger bone of St Anne, mother of Mary, it was an important pilgrimage destination in the Middle Ages. The tall nave dates from the 11th century, the choir, complete with glorious stained glass, from the 1200s. Locals say that if you squint at the rose window on the north side it appears to turn – another of Carcassonne's tricks of light and illusion.
I moved on to the castle. Incorporating a stretch of the western walls, Chateau Comtal dates from the 12th century and at first seems a disappointing series of empty courtyards. But the main reason for coming here is to walk the walls. This is the one part of the citadel where you can explore the ramparts and take in the remarkable medieval defence systems (albeit with modern reproductions). The views, too, are amazing. I gazed over the River Aude and the lower town of Carcassonne, and stretched my eyes across the landscape of Languedoc.
It was because of the Albigensian Crusade that the land of the Occitan people became part of France. The pope's army was provided by the barons of northern France, and ultimately the French king Louis IX took control of the region. The triumphant Louis orchestrated the building of Carcassonne's lower town, the Bastide, in the latter 13th century. It's an old-new town that provides an appealing contrast with La Cité above. While the citadel is now a dramatic tourist venue, lined with souvenir shops and restaurants and containing just 50 or so genuine residents, the Bastide is full of contemporary life. I browsed the morning market at Place Carnot – awash with vegetables, flowers and honey stalls on Tuesdays, Thursdays and Saturdays. I ambled along Rue de Verdun, lined with galleries and enticing shops. (The Musée des Beaux Arts, at number 1, offers free admission, as does the Chapelle des Dominicaines at number 19, now housing an exhibition on the Bastide's architecture.) I strolled north to the Canal du Midi where a couple of boating outfits were gearing up for the start of the cruise season along this historic waterway.
Of course, there are plenty of other trips to make from Carcassonne, for this two-tier town is the gateway to prime Cathar country. The land around still resonates with the story of the martyred sect and is dotted with the remains of castles that belonged to the Languedoc lords who defended the Cathars. One of the most striking such sites is half an hour's drive north of Carcassonne. At Lastours in the craggy Black Mountains, the ruins of four castles stand tall over a rocky ridge. They were erected in the late 13th century as a show of domination by the conquering French. Three of them were built just above the sites of three Occitan castles. These, together with villages where Cathar people lived, had been destroyed by the invading troops. The area is now an archaeological zone.
On the day I was there it took about two hours to walk around the ruins, a dark sky adding to the brooding atmosphere. Happily there was a treat at the end of my circular trail: Lastours is home to a Michelin-starred restaurant whose chef, Jean-Marc Boyer, also runs what he terms a country "auberge". It's a delightfully modest description, for at L'Auberge du Diable au Thym you'll enjoy an epicurean feast – at pleasing low prices.
'Labyrinth' by Kate Mosse is published by Orion. The television adaptation of 'Labyrinth' airs on Channel 4 on 30 and 31 March at 9pm
Ryanair (0871 246 0000; ryanair.com) flies to Carcassonne from Bournemouth, East Midlands, Glasgow, Liverpool and Stansted.
For luxury and history, check into Hotel de la Cité (00 33 4 68 71 98 71; hoteldelacite.com). Doubles from €195 room only.
Hotel Mercure Porte de la Cité (00 33 4 68 11 92 82; mercure.com) is near the citadel. Doubles from €168 room only.
Hotel Terminus (00 33 4 68 25 25 00; soleilvacances.com), opposite the railway station, offers doubles from €110 room only.
Brasserie le Donjon (00 33 4 68 25 95 72; brasserie-donjon.fr) at 2-4 rue Porte d'Aude offers regional dishes. €23 for two courses.
Restaurant Le Richepin (00 33 4 68 25 36 10; hoteldescouronnes.com), Hotel des Couronnes, 2 rue des Trois Couronnes, has views of the fortress skyline. €25 for two courses.
L'Auberge du Diable au Thym (00 33 4 68 77 50 24; lepuitsdutresor.com) is at 21 route des Chateaux, Lastours. Lunchtime menus from €15.
Chateau Comtal (00 33 4 68 11 70 70; carcassonne.monuments-nationaux.fr) open daily, €8.50.
Les Quatre Chateaux de Lastours (00 33 4 68 77 56 02; chateauxlastours.fr) open daily, €6.
00 33 4 68 10 24 30; carcassonne-tourisme.com
00 33 4 68 11 66 00; audetourisme.com