Hello my friends dug and found a tunnel and suspect it to be of jap making . it is close to a bridge near a former concentration camp . It is about 20 ft deep and the tunnel is half a circle at the base and inverted V shape on top with concrete lining some parts of the top portions are already falling apart . The tunnel crossed the brook and about 50 ft long. We just want some feedback as to. The.best way to operate this.venture. Thanks