Shadows of the Old Castle (1966)

A mysterious castle has stood on the island for 300 years, about which there are many legends and rumors. In reality, the castle is home to a boarding school, but local residents are sure that the ghost of the Green Hunter lives there. The boys also think they hear footsteps at night. And they were not mistaken - their search for adventure leads them to the sinister secrets of people who collaborated with the Nazis during the war.