Portal: No Escape is an incredible Portal-based short film directed by Dan Trachtenberg with visual effects by Jon Chesson and starring Danielle Rayne. Independent of whether or not you’ve seen or played the game*, this is really cool.
* The loose concept behind the game is that you have a gun which, upon shooting once, creates an exit portal and, upon shooting again, creates an entrance portal. Go through the entrance portal and you pop out the exit portal. Shooting a third time creates a new exit portal while erasing the existing entrance and exit portals.