The "Gate", also referred to as "the rift", is a portal to the Upside Down located in the underground subsystem of Hawkins National Laboratory. It is large, sprawling and consists of an assortment of strange tendrils, membranes and toxic biological growth.
Unlike other portals the Gate stays permanently open with the Upside Down growing out of it, expanding into the laboratory. The Gate disrupts the electromagnetic field, causing compasses to point toward it instead of the Earth's magnetic north.
A test subject with psychic powers labeled Eleven was instructed by Dr. Martin Brenner to make contact with the Monster. She was placed in a sensory deprivation tank at Hawkins National Laboratory which allowed her to become immersed in a deep psychic state, amplifying her abilities. When Eleven touched the Monster, the Gate cracked open in the wall of the tank room. The opening allowed the Monster to travel out of the Upside Down and into their dimension. Amidst the ensuing chaos, Eleven escaped the lab.
The area of the lab in which the Gate opened was immediately contained and quarantined. The following day, Dr. Brenner and several scientists went underground wearing hazmat suits and discovered that the Gate was expanding into the lab.
Dr. Brenner sent Shepard, one of his employees, into the Gate to investigate. Attached to a security line so that he could be pulled out in the case of an emergency, Shepard was soon attacked by the Monster. The Hawkins Lab workers were unable to pull him to safety in time, and he died.
Lucas Sinclair, Mike Wheeler, Dustin Henderson, and Eleven attempted to find the Gate using compasses, but Eleven directed the compasses away from the laboratory. Lucas continued the journey on his own but was forced to stop after he was unable to pass the wire fence surrounding the laboratory.