Science Festival 2026 in Vexin (95): discover the landscapes on geological walks

Head out to explore the landscapes of the French Vexin through a series of geological walks held across the region on October 3, 4 and 11, 2026, as part of the new edition of the Science Festival.

Each year, the Science Festival invites the public to discover science in a new light. Held across France, this free event brings together hundreds of activities imagined by researchers, associations, museums and local authorities. From 2 to 12 October 2026, the festival returns with a new edition under the theme "Savory Science". Workshops, walks, experiments and encounters make scientific topics tangible for both enthusiasts and the simply curious. In Île-de-France, several sites take part in this grand celebration of knowledge, including the Parc naturel régional du Vexin français, a territory where geology, landscapes and the environment become real fields of observation. Guided outings to discover them on October 3, 4 and 11, 2026 (details in the program).

Created in 1995, the Parc naturel régional du Vexin français covers nearly 99 municipalities in the Val-d'Oise and the Yvelines. It was established to protect a rural area with strikingly well-preserved landscapes, while supporting its development. Between agricultural plateaus, valleys, limestone cliffs, rivers and charming villages, the park also safeguards a rich historical heritage, with churches, mills, castles and archaeological sites. These landscapes have inspired many artists, notably the Impressionist painters, drawn by the light and the panoramas of the Vexin.

The Vexin Français Regional Natural Park provides an ideal setting to talk about geology, water, scenery, and the environment. Valleys, chalk cliffs, quarries, and old mills vividly illustrate how the landscape formed and how people used it through the centuries. The Science Festival makes it possible to explore these topics directly on the ground, using elements that are visible and easy to understand. An accessible way to better read the Vexin’s landscapes and to connect the natural sciences, heritage, and local history.

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The 2026 Science Festival program in and around the Vexin Regional Nature Park

A geological stroll in Chars
Chars is renowned for its troglodyte architecture and its mills, making it the perfect setting for water and stone to converse. The route begins in the village and continues along the right bank of the Viosne.
The valley is carved into Lutetian limestones (the transition from middle to upper Lutetian is visible in several spots). The valley floor hosts a remarkable wetland protected as a Sensitive Natural Space (C.D. Val d’Oise). The path goes beyond the Moulin de Noisement to a garden transformed into an “edible forest” by the Noisette association. We then climb to the right into an adjacent valley and its stream up to its source. The old pumping station located above provides a chance to explain the village’s past and present water supply.
Returning via the plateau offers splendid panoramas of the Vexin’s ridges (the Molière buttes of Serans, Rosne and Marines).
Participation conditions :
• Target audiences : 11–15 years, 15–18 years, 18–25 years, 25 years and up
• Requirements : Booking required
Schedule: Sunday, October 4 – 10:00 to 12:30

Geology tour of Vaux-de-la-Celle
The Vallon des Vaux-de-la-Celle is a standout geological curiosity in the French Vexin. This geology, by the way, is closely tied to the Gallo-Roman settlement… Between rock and water, two geologists from CY Cergy Paris Université invite you to explore the subsurface, the landscape, and the geological processes at work on the archaeological site.

Open to the general public (adults and children aged 8 and up)
Participation requirements:
• Target audiences: 11–15, 15–18, 18–25, 25 and up
• Requirements: Booking required
Schedule: Saturday, October 3 — 2:30 PM to 5:00 PM

A Geological Stroll in Perchay
The walk will begin at the top of the ravine, where a natural funnel collects runoff from the Vexin plateau.
Another feeding source comes from the waters of the village’s wastewater treatment plant at the head of the ravine. The very steep slopes of this site reveal striking natural cross-sections of the “Calcaire Grossier” from the Lutetian (the Vexin stone). As we descend the Vallée aux Moines, we will observe and explain the numerous springs (often paired with washhouses) that mark the emergence of the “nappe phréatique de l’Eocène” and feed the river. With archival photos, the usual peaceful scene will be contrasted with the catastrophic events (floods and mudflows) that occur several times per century. We will also show that the valley’s morphology points to ancient landslides. We will then reach the Couleuvre valley and the Vallière pond, where a remarkable geological site displays the transition from the “sables de Cuise” (Ypresian) to the “Calcaire Grossier” (Lutetian). Along the way, we’ll also note the village’s building stones (grossier limestone, sandstone) and mention the hydraulic rams that once supplied water to the village.

RDV : at the top of the ravine (parking available on the path leading to the wastewater treatment plant); return to the starting point will be organized by carpooling.

Participation requirements:
• Target audiences: 11–15, 15–18, 18–25, 25 and up
• Requirements: Booking required
Hours: Sunday, October 11 — 10:00 AM–12:30 PM

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