Geography & environment :
Situated at an altitude of 1150 m, in the heart of the village of Les Rousses and the Haut-Jura Regional Nature Park, the Fort des Rousses is the 2nd largest fortress in France. Access to the exterior of the buildings, the parade ground and the moat tour is free. Activities and visits are subject to a charge.
A little history:
In 1815, Napoleon returned to power and the allied European powers prepared to invade France. The Col de Saint-Cergue, then Les Rousses, was one of the main entry points. In response to this threat, orders were given to fortify the village. Several redoubts were built. One redoubt can still be seen in the village of Les Rousses. It was at the centre of the Battle of Les Rousses in July 1815. But it was not until 25 years later that work began on the Fort des Rousses. A natural mound near the village, the Cernois, was chosen as the site. Work continued for around twenty years, and the fort went into service in 1862, housing a brigade. In 1868, 81 artillery pieces were installed. The fort was used by the military until 1919, when it was abandoned. In 1925, and from 1930 to 1938, the fort was used as a holiday camp. From 1939, it was once again used by the military, but it was the Germans who occupied it. The Maquis regained possession of the fort in 1944 following the Battle of Turu. The fort became a commando training centre until June 1997, when the State sold it to the commune of Les Rousses. It was then renovated to house the Juraflore maturing cellars, the offices of the Les Rousses Resort Community of Communes and the Les Rousses Resort Management Company.

A variety of activities are available on the Fort des Rousses site, depending on the season:
Guided tour of the Juraflore Comté cheese maturing cellars: http://www.lesrousses.com/a-voir-a-faire/culture-et-patrimoine/caves-daffinage-comte.html
Commando Games activities: course, orienteering missions, precision, and crossing .... relive the military past of Fort des Rousses :https://www.lesrousses.com/a-voir-a-faire/activites-et-loisirs/commando-games-au-fort-des-rousses.html
Permanent Orienteering course, marked out in Gold: http://www.lesrousses.com/a-voir-a-faire/activites-et-loisirs/parcours-dorientation-baliseor.html
Hiking: signposted walking trail to discover the Fort des Rousses and one of the old redoubts from the Les Rousses Tourist Office. Route sheet available from the Tourist Office (sheet no. 16) or download: http://www.openrunner.com/index.php?id=1835515.
Mountain biking: signposted circuit to discover the Fort des Rousses from Les Rousses Tourist Office. Route sheet available from the Tourist Office (sheet no. 2) or download: http://www.openrunner.com/index.php?id=2054050
Around the Fort by the moat: an easy 3km walk (white stony path). In winter, the Espace Liberté "Le tour du fort" is an easy 3km groomed trail with free access for all kinds of activities: https://www.lesrousses.com/a-voir-a-faire/glisse-et-activites-neige/espaces-recreatifs/espaces-liberte.html
The Soldier's Trail: discover the history of the Fort des Rousses, how it works and its environment on the discovery trail around the ramparts. This short circuit, easily accessible to all, on trainers or snowshoes, is an ideal and fun walk for the whole family, punctuated by explanatory panels. Drop in at the Tourist Office in Les Rousses before you set off: children will be given an "ordre de mission", a fun document to accompany them on their discovery.
To find out more about the site, ask for the document on the history of the fort.
A book on the history of the Fort was produced by Les Rousses Town Hall in October 2019. It is on sale in the resort's Tourist Offices.