Interstice

A girl goes missing while on a camping trip to one of The United States National Parks with a group of others. A search and rescue team is deployed in an attempt to locate the missing girl, but what was found instead was something of far greater concern: Amidst a forest clearing, a black door, freestanding and leading seemingly nowhere. Upon opening, it reveals a black hallway which overlaps with reality.

A man belonging to a secret organization that documents anomalous phenomena is forced to investigate the door, discovering the horror within.