This Maginot Line fort, rather deep making it more like a bunker than a fort, is located near the village of Soufflenheim in Northern Alsace.
Visiting the Soufflenheim Fort is not for the faint of heart, there are 263 steps down into the bunker with no elevator to get you back up. Once down in the bunker it can get somewhat claustrophobic, as some of the tunnels are narrow. The bunker is a constant 53 degrees so bring warm clothing. You will also do some walking as the bunker has over a almost a mile of tunnels.
Tours are self-guided, there is not too much documentation, but that really should not take too much away from your visit, as most of what you see is self-expiratory. You will be able to see the fort's command center, 100-ton cannon (You can rise and lower it.), and solders quarters. The fort's train system is still entacked so you can see the cars and tracks.
Plan for two hours to view the fort. Entry is 5 euro with children under twelve 3 euros and under three free.