Did you know that under the trees in a park in the capital of inland navigation lies a rarely accessible medieval treasure? Each autumn, the Heritage Days stirs the curiosity of Ile-de-France residents by opening sites that are usually off-limits. For this 2026 edition, head to the Yvelines, at Conflans-Sainte-Honorine, where the park of the Château du Prieuré unveils one of its oldest secrets: its Grand Cellar. An invitation to swap Parisian asphalt for a living dive into the region’s river-and-monastic history, at the confluence of the Seine and the Oise.
Before it became the bourgeois residence seen in the 19th century, the estate housed an influential Benedictine priory. According to tradition, this spiritual haven was founded to safeguard the precious relics of Saint Honorine, hidden here in the 9th century to escape Viking raids. The ensuing pilgrimage gave a powerful boost to the medieval town.
Though the Revolution and successive reshuffles erased most of the monastery, the Grand Cellier, built in the 13th century, has withstood the test of time. Listed or registered as a Historic Monument according to the parts of the estate, it once served as a warehouse for provisions and the monks' wine production.
To step into the Grand Cellier, you sense the full ingenuity of 13th‑century builders. Far from the dimness of a ordinary cellar, the space is defined by its Gothic vaulting with ogival arches. This system of cross-ribs transfers the weight of the stones onto solid pillars and corbels integrated into the walls, freeing a generous ceiling height and a surprisingly ample volume.
Today, safeguarded by the municipality and integrated into the Prieuré cultural complex, the site has swapped its wine barrels for a very different cargo. It now serves as the showcase for the museum's collection of leisure craft and antique canoes of the Musée de la batellerie et des voies navigables, forging an unprecedented dialogue between river heritage and centuries-old vaults.
Ready to explore these vaulted galleries and let the memory of the place carry you away? Below you'll find the details of the time slots, guided tours, and activities planned for this historic stop.
Guided Tour of the 13th-Century Grand Cellar
Exceptional opening of the great 13th-century cellar, an architectural relic of the former priory normally closed to visitors. Now housing the collection of pleasure boats at the Museum of Inland Waterways, this site, with its preserved architecture, stands as a patrimonial showcase of notable interest.
Participation conditions: Free admission - No reservation required
Hours: Saturday, September 19, 2026 – 10:00–19:00 | Sunday, September 20, 2026 – 10:00–19:00
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Dates and Opening Time
From September 19, 2026 to September 20, 2026
Location
The Priory’s Grand Cellar
Rue du Prieuré
78700 Conflans Sainte Honorine
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