WARSAW, Poland (AP) — A Polish explorer claims he has found massive underground structure in southwestern Poland that, he says, the Nazis built as a nuclear shelter for Hitler.

Krzysztof Szpakowski told a news conference Friday he has "no doubt" as to his find, which he says was based on evidence that he has gathered for decades, including witness statements, old documents and an examination of the area by ground-penetrating radar and by dowsers.

Speaking on TVN24, Szpakowski said the structure was part of a system of railway tunnels and corridors that the Nazis were building during World War II around the city of Walbrzych. His conference was hosted by Walbrzych regional authorities.

Two other men claim they have fund another tunnel at a separate location in Walbrzych that contains a Nazi train.