Castel Val, Art Nouveau house in Auvers-sur-Oise, France

Castel Val is a house at 4 rue des Meulières on the Chaponval hill in Auvers-sur-Oise, built in 1903–1904 by architect Hector Guimard for Louis Chanut. Its asymmetrical massing combines pale rendered masonry with round and segmental windows, a half-timbered projecting section on a grey stone base, three triangular dormers and a tall red-brick chimney. An open porch with columns and a balustraded balcony stands above a round-arched doorway with a red door in rough stonework.

The villa was designed and built by architect Hector Guimard between 1903 and 1904 for resident Louis Chanut, who had connections to industrialist Leon Nozal. This construction stands as one of Guimard's villa projects created beyond Paris's central areas.

The name Castel Val refers to a castle in the Méran valley recorded by Édouard Charton in 1837, dismantled and abandoned over time. The house's rounded, backed-against-the-hill form has been read as an escargot, perhaps a nod to the owners' zoological tastes: they kept a dressed monkey called Mademoiselle. The original stained glass survives, while a fireplace is now in a Philadelphia museum and a chair at the Musée d'Orsay.

The house sits on Rue des Meulières and is easily recognizable from the street by its distinctive brick and iron details. Visitors should note that the protected gardens may not always be open to the public, so advance planning is recommended.

The residence contains numerous hidden passages and secret doors that allow access to outdoor spaces from different floors. These concealed features reveal how Guimard merged practical needs with artistic expression in the home's design.