We visited this fortress in 2009. Situated at an altitude of 775 m it is the highest situated building we visited yet. Although visited in March there was snow everywhere which was really cool!
Warning: If you plan to visit french military domains, know that the french police has a strict policy. If you get busted you will have to pay a big fine right away, otherwise your stuff (car etc.) will be taken by the police.
After the war against Prussia, France lost its Elsace and Lorraine provinces to Germany. The new border had to be protected with new fortresses. The general Séré de Rivières drawed up a plan. The plan contained two fortified lines, one along the hights of the Meuse between Verdun and Toul, and one line between Epinal and Belfort. This fortress is situated between Epinal and Belfort.
The fortress was built from 1874 to 1876. In 1890 a underground storage was added. In the first world war the fortress did not take part. This was due to the military plans of France (plan XVII) and the Von Schlieffen-plan of the Germans. The German plan considered a retreat in the former French areas, in order to lure away troops from the north. In the north of France the Germans wanted to advance, through Belgium, to Paris. The French plan was to attack and retake the lost provinces, which they did. The battles took place at the edge of the vosges. After the war the fortress was useless. It is still owned by the French army.