Aqueduc d'Azille
19th century aqueduct with ~ 30 arcs for irrigation purposes.
Each edition grades its towns against each other only.

Châteaux or heritage sites make up 5 of the 7 places on the list. None of them is inside Castelnau-d'Aude itself. Côte magnétique, 13 km away, is the best-known day out.
Behind Aqueduc d'Azille on the list are 5 châteaux.
Best known first: by how many Wikipedia and sister-site articles cover each place (Wikidata’s count). It isn’t a ranking of how good they are.
Château de Puichéric marks the outer edge, 4.1 km away.
The first 20 on the list, numbered as below. The shape is the commune of Castelnau-d'Aude; the orange dot is its centre. © OpenStreetMap contributors · commune boundary: IGN
5 châteaux or heritage sites and 2 other sights top the count.
Dark: in Castelnau-d'Aude. Light: in the communes within 5 km of its centre.
Its 7 places all lie within 5 km of its centre.
Nothing is mapped in Castelnau-d'Aude itself; these are within 5 km of its centre.
The history of Castelnau-d'Aude → · Parks and trails in Castelnau-d'Aude →
Côte magnétique, 13 km away, is the best known of the 12.
AttractionCité de Carcassonne25 km west, in Carcassonne
AttractionVoie Domitienne27 km east, in Narbonne
AttractionAbbaye Sainte-Marie de Fontfroide22 km southeast, in NarbonneCathedralCathedralCathédrale Saint-Just-et-Saint-Pasteur de Narbonne27 km east, in Narbonne
AttractionCathédrale Saint-Michel de Carcassonne26 km west, in CarcassonneAttractionAttractionAbbaye de Sainte-Marie de Lagrasse16 km south, in Lagrasse
ChurchBasilique Saint-Nazaire-et-Saint-Celse de Carcassonne25 km west, in CarcassonneAttractionAttractionPic de Nore27 km northwest, in Pradelles-CabardèsAttractionAttractionChâteau de Termes27 km south, in TermesChâteauChâteauChâteaux de Lastours27 km northwest, in Lastours
AttractionPalais des archevêques de Narbonne27 km east, in NarbonnePlaces within 40 km of Castelnau-d'Aude with an article in both French and English Wikipedia, nearest first.
Nothing is mapped in Castelnau-d'Aude itself, but within 5 km there are Aqueduc d'Azille, Château de Roquecourbe-Minervois, Château de Puichéric and Château de La Redorte.
No museum or gallery is mapped in Castelnau-d'Aude or within 5 km.
The nearest with articles in both French and English Wikipedia: Côte magnétique (13 km), Cité de Carcassonne (25 km), Voie Domitienne (27 km), Abbaye Sainte-Marie de Fontfroide (22 km).
From OpenStreetMap and Wikidata: named museums, galleries, châteaux, abbeys, gardens, zoos, theme parks and other visitor attractions whose mapped point lies inside the commune of Castelnau-d'Aude, then those in the communes within 5 km of its centre, and well-known places within 40 km. Houses, ruins and gardens need a sign they’re open to visitors; places marked private, closed or disused are left out. The historic-monument link is the Culture ministry’s Mérimée record. A place that isn’t mapped isn’t listed, so this isn’t everything there is to see.
Sources: OpenStreetMap (© OpenStreetMap contributors, ODbL), Wikidata (CC0: descriptions, websites, Wikipedia articles), the Culture ministry’s Mérimée database (Licence Ouverte 2.0), IGN commune boundaries. Distances are from the commune’s centre point.
Photos from Wikimedia Commons, each under its own licence (our copy, resized).
Contains public sector information under the Licence Ouverte / Open Licence 2.0 (Etalab): INSEE, DGFiP, the Interior Ministry’s statistics service (SSMSI), the Ministry of Education (DEPP), the Health Ministry’s statistics service (DREES) and the Housing Ministry (Carte des loyers). Commune boundaries: IGN Admin Express.