Grottes de Neptune

Grottes de l'Adugeoir - Grottes de Petigny

Useful Information

Location: Rue de l'Adujoir 24, 5660 Couvin.
At the motorway N5 (E420) between Charleroi and Charleville-Mézières, exit Chimay Couvin-Nord. Signposted from the roundabouts, follow road to Petigny, after 500 m turn right, 250 m to the parking lot. 5 minutes walk to the cave entrance along the river.
(50.066015, 4.512875)
Open: APR to JUN Sat, Sun 10-18.
JUL to mid-SEP daily 10-18.
Mid-SEP to mid-NOV Sat, Sun 10-18.
During Belgian School Holidays daily.
Fee: Adults EUR 9, Children (4-12) EUR 5.50, Children (0-3) free, Students EUR 8, Seniors (60+) EUR 8, Disabled EUR 8.
Classification: SpeleologyKarst cave Speleologyriver cave.
Light: LightIncandescent Electric Light System LightColoured Light LightSon et Lumière
Dimension: L=1627 m, VR=25 m, T=12 °C.
Guided tours: D=45 min, St=80, Max=32. Français - French Nederlands - Dutch English
Photography: not allowed
Accessibility: no
Bibliography: M. Dethier, J. Depasse (2007) La faune invertébrée des grottes de Neptune (anciennement Adugeoir) et du Pont d'Avignon (province de Namur, Belgique) Bulletin des Chercheurs de la Wallonie, 46: 97-108. Français - French
Address: Grottes Neptune, Rue de l'Adujoir 24, 5660 Couvin, Tel: +32-60311954, Fax: +32-60399771. E-mail:
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.


1888 discovered by PeopleE.A. Martel.
1932 electric light.
1952 opened as a show cave.
1972 sound and light show and boat trip added to the tour.
1980 renamed Grottes de Neptune.


The Grottes de Neptune (Neptune Caves) is a swallow hole or sink. The small river called Eau Noire (Black Water), a tributary of the Meuse river, meanders through its valley and flows right in front of the cave entrance at the foot of a limestone cliff. A part of the water is swallowed by the cave and reappears some 3 km further on, at the Résurgence de l'Eau Noire in Nismes, which is also worth a visit. It has a cave behind, called Grotte du Pont d'Avignon (Avignon Bridge Cave). It was explored very intensive, even by digging an artificial tunnel, but only 215 m of cave could be explored. It is underwater and too narrow for diving. Grottes de Neptune was originally called Grottes de l'Adugeoir in Belgian French, or Grottes de l'Adujoir, which means cave of the sink. It was also known as Grottes de Petigny, named after the nearby village. The karst area where it is located are low hills called Calestienne consisting of Middle and Upper Devonian (Frasnian and Givetian) limestones. The hill which is crossed by the river is called Les Rocailles (The Rocks) or Les Monts (The Hills).

The cave ceiling becomes lower right after the entrance, and so the river cave is hard to visit and requires swimming and some diving. The first to enter this cave was the famous French speleologist PeopleE.A. Martel in 1888. He also discovered the upper levels of the cave, which have no natural entrance from the surface.

After the survey of the cave the location of the passages was known, and in the 1930 the cave was developed as a show cave. A 200 m long tunnel was dug between the fossil level with beautiful concretions and the active level with the river. Here a boat is entered and this level is visited on a twenty minutes boat trip. They are very prod of the coloured light and the light show at the end.

The cave is owned and operated by the commune of Couvin. The cave is home to different species of bats and numerous troglobionts. It is protected and part of the Natura 2000 network. Since Corona they sell tickets online, so open hours are managed by the online booking system on their website. ExplainPost-pandemic Aftermath But the combo ticket with nearby Abime was discontinued.

A guided tour takes the visitor on a journey of discovery in a natural setting of stunning beauty, along the foot of shimmering limestone cliff.

A walkway overlooking the wild and meandering river "Eau Noire" [The Black Water], crosses in front of an impressive porch which swallows up the river. The visit continues into the two upper galleries of the Caves of Neptune, with their superb rock formations sculptured by nature. The visit culminates in a 20-minute boat ride along an underground river, 10m below the level of the "Eau Noire". The journey is enhanced with an unusual "music & light" display, which, it is claimed is unique in Europe. During this display there are a number of lively waterfalls which form an impressive backdrop to the scene. The music of Vangélis and the stroboscopic light effects makes this a truly magical event which will live in the mind of the visitor forever.

Text by Tony Oldham (2002). With kind permission.