It is currently being guarded by Obsidian, the last of the Order of the Obsidian, a group of Gem mystics who sought to understand existence and the meaning of life in the universe as well as hiding the Doorway.
It is unknown how the rift that would become the Doorway came to be. The mystical Order of the Obsidian discovered it thousands of ago when they were seeking a place of solitude where they could acquire the knowledge of the meaning of existence. Due to its highly unpredictable nature and the potential danger it may pose, the Obsidians kept the rift a secret and built their sanctuary over it in order to keep it hidden. They were especially committed to keep this site hidden from the Great Diamond Authority, due to the implications it could have for rapidly expanding the Gem Empire in this world and into other dimensions.
After the Rebellion on Earth, the Order of the Obsidian was all but destroyed in retaliation for their role in aiding the Crystal Gems. Its members, though all except Obsidian lost their lives, fought and managed to conceal the Doorway from Homeworld, and even long after the place and order were forgotten Obsidian continues to stand as its solitary sentinel to this day.
The Doorway connects to several far distant points in this universe as well as alternate realities. Of the ones located in this universe, it is the one nearest to any place the Gems are aware of and traveled to, and certainly the closest to Earth. Though it is connected to other wormholes, the place it leads to randomly changes over time. For instance, if two people were to enter it in succession, regardless of the time between them, chances are they will end up at different places or different dimensions. This is not guaranteed though, but it can make returning to one's own universe difficult.
In addition, the Doorway can also serve as a window, merely allowing others to view into it. According to Obsidian, it shows multitudes of worlds simultaneously, and it takes a highly trained mind to pinpoint a desired location to observe.
- Olympus Mons is a volcano located on the planet Mars. It is the largest volcano in the known Solar System.
- Curiously, it acts as a one-way route for travelling within this universe, but one can travel back and forth between alternate realities. That is because there is one such portal located in each dimension, though the one through which the traveler comes out of is uncontrollable and only determined by chance.