The Col-des-Roches Underground Mills, in Le Locle, are water mills built in a cave in the 17th century, 23 m underground. You follow a route through galleries where the reconstructed wheels, millstones and mechanisms run on water power.
Themed museums
Main highlights
- Underground water mills built from 1660 onwards in a karst cave at Col-des-Roches
- 150 m route at a depth of 23 m, with faithfully reconstructed installations
- Working water circuit that turns the wheels and shows the mechanisms in action
Overview
In the 17th century, the western part of the Le Locle valley was a marsh where the Bied flowed too slowly for a conventional mill. However, the water plunged into the Col-des-Roches sinkhole, forming a waterfall. In 1652, three pioneers installed two wheel systems there, then from 1660 Jonas Sandoz had the cave excavated to house five wheels powering mills, a sawmill, a hemp-crushing mill and an oil press.
The site operated as mills until 1884, became a slaughterhouse in 1898, then closed in 1966, heavily polluted. From 1973, the Confrérie des Meuniers du Col-des-Roches restored it on a voluntary basis over fifteen years and opened it to the public in 1987.
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What to see and do
The visit begins above ground in a museum area. A permanent exhibition presents the history of the mills and the Le Locle region, with period documents, authentic objects and information panels on the challenges faced by the builders.
You then descend 23 m underground into a network of natural and man-made galleries and tunnels. The 150 m route runs past the water wheels, transmission mechanisms and stone millstones. Underground channels carried the water from wheel to wheel, while galleries and staircases were used for maintenance. A working water circuit turns the wheels, and the former sawmill has been showcased.
Audio guides in French, German, English and Italian describe each feature. Public guided tours add anecdotes about the millers’ lives.
Practical information
Getting there : from Le Locle station, take the PostBus to the “Moulins souterrains” stop. On-site parking for cars.
Visit duration : about 1 hour.
Visitors : the visit is not suitable for people with reduced mobility (stairs, humidity). Dogs not allowed. Groups welcome by appointment.
On site : audio guide included with admission and a tourist office on the premises.
Visiting tips
The cave stays at 7 °C all year round, with high humidity. Bring a warm, waterproof jacket, even in summer, and closed non-slip shoes, as the ground can be slippery.
For more detailed explanations, arrive in time for a public guided tour rather than visiting on your own with the audio guide.
Nearby
- The Le Locle Museum of Fine Arts brings together fine arts, graphic arts and contemporary works.
- The Saut du Doubs is a waterfall on the Doubs, on the French-Swiss border, which you can explore on foot or by boat.
- The Le Locle Watchmaking Museum showcases mechanisms, complications and rare pieces from Le Locle’s watchmaking history.
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