Serious sci fi, probably from 70-80s. Aliens land, there is a huge ship on the ground. Humans try to infiltrate the ship, they are crawling through the alien airducts, the aliens have human like appearance and might be bald or not, finally the aliens notice that humans are in the airducts and attack them/kill them. The aliens might have long tongues, but im not sure, its hazy. I posted this on this site but i didn’t get an answer. It’s driving me nuts for the last 20 years. It might have been a movie or a series, but it was scary and dark, also literally dark.