Besseringen B-Werk, Armoured bunker of the Siegfried Line in Merzig, Germany

Besseringen B-Werk is a three-storey armoured bunker of the Siegfried Line in Merzig, built 1938–39 with walls and ceilings 1.5 metres thick. Its 44 rooms cover a floor of 24.60 by 17.80 metres, and two six-port turrets, an observation cupola and a grenade-launcher turret sit on its roof. Inside, a long concrete corridor with exposed pipes and a metal grate walkway leads past red metal fittings and a green EXIT sign.

The B-Werk at Besseringen was built in 1938 and 1939 as part of the Siegfried Line, the 630-kilometre defensive system erected on Germany's western border between 1936 and 1940. It cost about 1,300,000 Reichsmarks and used roughly 2,800 cubic metres of concrete and 200 tonnes of steel. Of the 32 B-Werke planned, it is the only one preserved complete with all its weapon cupolas.

The name B-Werk comes from construction standard B, meaning walls and ceilings 1.5 metres thick; officially the site was called Panzerwerk or given a codename so the enemy would not learn its strength. Inside, visitors see the two six-port turrets, the observation cupola and the M 19 grenade launcher turret, which projects only 0.30 metres above the roof.

The B-Werk is entered on its upper level; inside, a long concrete corridor with a metal grate walkway along the floor and pipes and a large duct overhead leads past doorways to the far end, where a green EXIT sign marks the way out. The three-storey layout means stairs between levels, and the low ceilings and narrow passages call for a torch and sturdy shoes.

This structure is the only one of its kind that has retained its original form to this day and still has all its important features intact. Most other similar installations were destroyed or heavily altered.