La grotte des Petites-Dalles

Useful Information

Location: Saint-Martin-aux-Buneaux 67 (Seine-Maritime).
(49.815709, 0.531808)
Open: On open days 10, 14, 16.
Fee: Adults EUR 2.
Classification: Explain Karst cave.
Light: LightIncandescent Electric Light System
Dimension: T=12 °C, L=835 m, A=35 m asl.
Guided tours: L=400 m, D=1 h, Max=20, MinAge=8.
Photography: allowed
Accessibility: no
Bibliography: Joël Rodet, Jean-Pierre Viard (2007): A la découverte de la grotte des Petites Dales (Saint-Martin-aux-Buneaux - Seine-Maritime) Spéléo-Tract n°6, Juillet 2007, ISSN 0290-1412.
Address: Monsieur Jean-Pierre Viard, 97, rue du 8 mai, 27400 Montaure, Tel: 0683-326794 or 0232-506174.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
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1966 cave first explored by speleologists.
1989 beginning of excavation by the AC Renault-Cléon caving group led by Jean-Pierre Viard.
2017 awarded the Martel–de Joly prize by the French Speleology Federation.


The Grotte des Petites-Dalles (Cave of the Little Dales) is named after the nearby village Petites-Dalles, which is located in Saint-Martin-aux-Buneaux near Fécamp in Seine-Maritime in the Normandy. This area has Cretaceous chalk, similar to the Dover cliffs on the opposite side of the channel, which is normally not very good for karstification. The cave is not very spacious, but in 2021 it was explored for 853 m which makes it the longest cave in Seine-Maritime and the 8th longest in the Paris Basin. It is also the only show cave in the Normandie.

The entrance section has been known for a long time, locals and English tourists at the nearby seaside resort visited the cave and left inscriptions during the 19th century. Before World War II a tramp lived for some time in the cave. The local teenagers started to explore the cave and left marks how far they ventured. Finally, in 1966, the Caving Club of Rouen explored the cave. They surveyed the cave to be 62 m long, their results were published in Spelunca in 1967. It was visited by more speleologists, but in the 1970s several attempts and digging increased the cave length only by 10 m.

The cave passage is almost completely filled by loose sediment, like many caves in the Normandy. The sediment is mainly loess, introduced during the Pleistocene, and rather easy to remove, nevertheless it is a lot of work. From 1989 the AC Renault-Cléon caving group led by Jean-Pierre Viard started a massive excavation. Until today more than 3000 m³ of sediments were removed and the length of the cave has increased to 853 m [2021].

The cave is a show cave, but it seems there are no regular open hours and there are only a few open days during summer. There is also a website for online booking which gives the dates of the open days, for 2022 there were only two open days which have already passed. The easiest way to visit the cave is to make an appointment with Jean-Pierre Viard or to visit on the day of the yearly Cave Festival.