Rennes-les-Bains (French pronunciation: [ʁɛn le bɛ̃] ⓘ; Occitan: Los Banhs de Rènnas) is a commune in the Aude department in southern France.

Bathers have enjoyed the natural hot spring waters for thousands of years - they are still used today as a cure for rheumatism and certain skin problems.

Rennes-les-Bains is known for another reason, however: it is mentioned numerous times in many books about Rennes-le-Chateau, famous now also because of Dan Brown's novel The Da Vinci Code.

Boudet's strange book, La vraie langue celtique et le cromleck de Rennes-les-Bains (1886) argued that all languages were derived from the English tongue whereby the Abbé tried to establish his theory through the use of puns.

In 1832 a book by Auguste de Labouïsse-Rochefort entitled Voyages à Rennes-les-Bains first referred to a treasure located at Mont Blanchefort, whereby a story was told about a wizard who nearly succeeded in taking the purse-strings of the Devil, but failed because the local villagers did not help him at the crucial moment - Auguste de Labouïsse-Rochefort had married a daughter of a millionaire that had lost his fortune.