A former history teacher hopes to use ground-penetrating radar to uncover a network of Nazi tunnels believed to be beneath Oslo's city streets.

Øyvind Skarlund was once the head of history at Oslo's Handelsgymnasium, a public high school in the Norwegian capital, according to The Local. The school, a former headquarters for Nazi military leaders during World War II, has a Nazi bunker in its cellar which is now a memorial to the German occupation.

It was this introduction to underground Nazi construction that piqued Skarlund's interest in the possibility of exploring Oslo's reputed tunnel network....