The largest single Maginot Line bastion in the Metz area was the 1000-man Fort du Hackenberg, whose 10km of galleries were designed to be self-sufficient for three months and, in battle, to fire 4 tonnes of shells a minute. An electric trolley takes visitors along 4km of tunnels – always at 12°C – past subterranean installations. Tours last two hours. The fort is around 35km northeast of Metz via the D2 or A35.
The fort is probably best seen as a day trip from Metz – there's a smattering of places to eat in nearby Thionville.