I think there were lots of different underground levels in the research base.
When the soldiers went in, they found an unhelpful scientist (not a priest) on the first level.
They left him there with a soldier whilst other soldiers went to the lower levels.
They were then pursued by some kind of creature.
Can’t find this film anywhere. I only know that the film was NOT called The Devil’s Tomb. It was a film similar to that, though.