Rumors of hidden Nazi gold have sparked wild goose chases across Germany and neighboring countries since the fall of Adolf Hitler’s party in 1945. But one history teacher in Norway is interested in a buried Nazi treasure that can’t be hawked at a pawn shop.

Øyvind Skarlund, a retired historian, believes Norway’s capital city of Oslo sits atop a network of underground Nazi tunnels. Skarlund plans to search for the tunnels using ground penetrating 3D radar.

"The plan is to investigate if the tunnels really are there," Skarlund told The Local. "I've seen the plans for the tunnels from the war years, and I've also seen the plans for the bunker, and it seems likely that there is a second bunker underneath the one we have."

In 2000, the school where Skarlund taught, Oslo Handelsgymnasium, was given keys to a former Nazi bunker located in the school’s cellar. According to The Local, the building once served as the German military headquarters during World War II. The Nazis built a large bunker in 1941 beneath the school. The Norwegian military kept the keys to the bunker after the Nazis were expelled from Oslo four years later.

In 2000 the school made it into a memorial museum to the country’s Nazi occupation.

According to The Huffington Post, Skarlund only recently raised enough money through the Gimle Rotary Club to explore the hidden Nazi tunnels in Oslo. The project will cost roughly 200,000 kroner, or $30,000 USD.

Ground-penetrating radar uses radar pulses to map the subsurface of the Earth. Developed over the past 30 years, 3D ground radar can provide accurate depth estimates for all kinds of underground objects.

Three-dimensional radar has proven useful in a number of scientific fields. For geologists, ground radar helps them study bedrock, soil, groundwater and ice. Archaeologists use it to detect and map archaeological artifacts, features and patterning.