The aura of this building, its sheer monumentality, is overwhelming. The bunker is more than 400 metres long, more than 30 metres high, and almost 100 metres wide at its western end. It is the second biggest facility of its kind ever built above ground in Europe. Today its walls of black-stained concrete, partly overgrown with creepers, purvey a morbid atmosphere - a ruin, created as if for eternity. But this concrete monster and its surroundings were once places of terror. The construction of Bunker Valentin cost more than 1200 human lives. It was built by the National Socialists towards the end of the Second World War, between 1943 and 1945, using for the most part forced labour, including concentration camp prisoners and POWs. Conceived as an indestructible factory for submarines, its concrete walls and roof were several metres thick to protect it from Allied bombs. The submarines it would launch onto the River Weser would - at least that was the strategic plan - harass Allied shipping in the North Atlantic and bring about a late turn of fortune in the war. Copied from the Detroit assembly line, the planned production methods were state-of-the-art, envisioning a conveyor belt system with rapid turnaround, but the means taken to achieve that end were brutal and archaic. As in so many other settings of the self-designated Third Reich, the workers on the construction site were tormented without mercy and driven to exhaustion.