70/80s Movie: Nazi's have set up camp in a large cave that is also occupied by some sort of monster

I am trying to track down the name of a movie I watched many years ago. The scene is located somewhere in the WWII European theatre where a large formation of Nazis has set up camp in a large cave system near a small village. The twist is that the cave system is also home to some form of monster (devil) that is wreaking havoc on them. The main actor plays a father/priest and arrives in the village on a bicycle. He has come to investigate the strange behaviour. The main actor was popular within war movies of the time, in my mind I keep thinking it is Anthony Quinn, but can’t find anything in his movie list. Thank you

The Keep (1983)
starring Scott Glenn and directed by Michael Mann

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