Located a stone’s throw away from Thionville, Fort du Hackenberg is an eye-opener for history buffs and any who wish to visit ghosts of the past. One of the biggest among the Maginot Line fortifications, it was thought to serve as an indispensible defence line during World War I. The fort remains today as a museum that is as fascinating as it is inconceivable with its vast network of underground fortifications. Hop on an electric train to manoeuvre across artillery turrets the same way the soldiers used to, take time to marvel at the impressive museum of uniforms and weapons and basically be in awe of the seemingly impregnable fortress of bunkers, bastions and tunnels. Dress warm though, the tunnels leave you frigid even in the summer.