Grotte des Petites-Dalles

Grotte des Petites-Dalles is a karst cave in the commune of Saint-Martin-aux-Buneaux, in Seine-Maritime, on the Pays de Caux coast of Normandy near Fécamp. It is the only cave in Normandy open to the public for guided visits, carved into the chalky limestone layers of the coastal cliffs.

Where exactly is it?

The cave entrance sits at the foot of a former quarry, right on the road connecting Saint-Martin-aux-Buneaux to the neighbouring village of Sassetot-le-Mauconduit. A short drive away lies the beach of Petites-Dalles, framed by the tall Amont and Aval cliffs — the same coastline that drew Impressionist painters in the 19th century, including Claude Monet and Berthe Morisot.

How was it formed, and how big is it?

The cave had been known locally for a long time, but systematic speleological exploration only began in 1966. Since then, cavers from local associations have gradually pushed further into its passages, clearing away sediment deposits — mostly loess laid down during the Pleistocene. This clearing work has continued without interruption since 1989: groups of speleologists head underground on a weekly basis to keep excavating the galleries. The results of decades of volunteer effort are striking — by the end of 2021, the surveyed network reached a total length of 853 metres, making it the longest cave in the entire Seine-Maritime department and placing it among the eight longest chalk caves in the whole Paris Basin.

What will you see on a visit?

Visits are guided, with a group leader taking small groups through the excavated passages and explaining how water slowly carved the soft chalk over thousands of years, as well as how the ongoing clearing work by local speleology enthusiasts actually happens. It's a rare chance to walk through a cave that is still being discovered — this isn't a polished, fully lit show-cave, but a live research site opened up to visitors.

When should you go, and who is it for?

Guided tours run at set times during the day — typically around 10am, 2pm and 4pm — so it's worth checking ahead, since group sizes are limited. Children are welcome from age 8, accompanied by an adult, which makes the cave a solid choice for a family outing that mixes a bit of geology with time outdoors. After the visit, it's worth extending the trip with a walk down to the nearby Petites-Dalles beach and village, where a cluster of Belle Époque villas still stands, decorated with the characteristic lambrequins and ceramic details of the period.

Anything else worth knowing before you go?

Given the nature of the cave — damp, and narrow in places — comfortable footwear and a warm layer are worth packing even in summer, since underground temperatures stay constant and noticeably cooler than outside. Saint-Martin-aux-Buneaux and Les Petites-Dalles also make a good base for exploring the wider Pays de Caux cliffs, the scenic stretch of chalk coastline running between Fécamp and Saint-Valery-en-Caux.

Frequently Asked Questions

Is Grotte des Petites-Dalles the only cave in Normandy open to visitors? Yes, it is the only cave in the region offering regular guided public visits.

How long is the cave? By the end of 2021, the surveyed passages totalled 853 metres, making it the longest cave in the Seine-Maritime department.

Since when has the cave been explored? Systematic speleological exploration dates back to 1966, and clearing work inside the galleries has continued without interruption since 1989.

Is the cave suitable for children? Yes, children can join the visit from age 8, provided they are accompanied by an adult.