In order to be in the Occultum, the Occultum must be in you.
The Occultum is an artifact of divine origin. For centuries, it was housed in a temple until it was looted by invading Mongol hordes. The Occultum would eventually be traded on the black market. Around 2008/2009, the Occultum came into the possession of the Jacobson family, but when Hyram Jacobson's son fell ill, he traded it to the faith healer / angel Sister Jo in exchange for her healing his son. Jo later gave the Occultum to the demon Ruby with the plan for them to ride out the Apocalypse inside. Ruby was subsequently killed after hiding it and had refused to tell Jo where to find it, knowing too well that she can't be trusted.
In 2020, Castiel manages to contact Ruby in the Empty and recover the Occultum, which she had hidden a church guarded by hellhounds. When Jack consumes it, the Occultum briefly transports him to the Garden of Eden, where the serpent restores his soul. The Occultum is currently in the Men of Letters Bunker.
The Occultum, whose name is Latin for "hidden", has the appearance of an ornate orb, inscribed with an Enochian passage that reads, "In order to be in the Occultum, the Occultum must be in you." When used by a non-human entity through ingestion, it transports them to the Garden of Eden.