Fort d'Uxegney is part of the late-19th-century defensive belt built after France lost Alsace-Lorraine in 1871. Its armoured turrets, galleries, and gun positions show a very different side of Lorraine from churches and river towns.
The fort is just outside Epinal, so it is easiest with a car or bike. Opening times are limited and often tour-based; check ahead rather than assuming you can wander in.