The Cité de Carcassonne can be visited in 1 full day. Tour of the Lices (between the two walls, free, 45 min): panoramic walk with views over the ramparts, towers, countryside. Comtal Château (€9.50, 1h30 with audioguide): 12th-13th century architecture, inner ramparts, museum route on the Cité's history and the Albigensian Crusade. Saint-Nazaire Basilica (free): exceptional Gothic stained-glass (13th-14th centuries), considered among the most beautiful in southern France. Medieval lanes: rue Trivalle, rue Saint-Louis, rue du Plô (touristy but preserved). Narbonne Gate (main entrance, Dame Carcas statue).
The Bastide Saint-Louis (lower town, created in the 13th century after the Cité's capture by crusaders) is often forgotten but deserves the visit: Place Carnot (heart of the Bastide, Neptune fountain, market 3x/week), Saint-Michel Cathedral (13th century), Pont Vieux (14th century, pedestrian access to the Cité), Maison des Mémoires (local history museum).
Nearby: Lagrasse Abbey (40 km, Most Beautiful Village of France, 9th-century Benedictine abbey), Cathar castles (Peyrepertuse 1h, Quéribus 1h10, Aguilar 50 min — spectacular vestiges perched on rocky spurs), UNESCO Canal du Midi (by bike, 240 km from Toulouse to Sète, sections accessible from Carcassonne), Minervois and Corbières vineyards (estate tastings), Castelnaudary (35 km, French capital of cassoulet — to eat on site).
The events: Festival de Carcassonne in July (concerts in the Comtal Château antique theatre: pop, rock, classical, opera — €20-80), equestrian shows at the Lices in summer, 14 July fireworks over the Cité (one of France's largest, 25-minute spectacle), Carcassonne Carnival in February (medieval processions).