Here's a solid sci-fi short film called The Most Beautiful Day directed by Einar Kuusk. The story is set in the post-apocalyptic future, and it centers on a man trapped in a bunker. The only way he can get out is through a ventilation shaft, but there’s an alien creature trapped in it that he must face off with if he’s going to get out.
"A young man named Sherman survives the apocalypse in a soviet-style alternate reality and when trying to find his place outside an isolated city, gets stuck in an underground bunker."
The movie has a pretty lengthy build-up, but I still really enjoyed it. Maybe you will too.