Multiverse

The Multiverse, as revealed in "The Lich," is the set of distinct alternate universes, or "dimensions," of which the Land of Ooo, Earth, and the Adventure Time universe are a part of. Although many dimensions are implied or alluded to in "The Lich" and its follow-up episodes, "Finn the Human" and "Jake the Dog," a dimension known as the Time Room, which is said to be the source of all time, receives particular focus. The concept of a multiverse is based on the popular real-world idea that several parallel universes may exist, with different physical laws, histories, and/or dimensionalities.

Map of the Multiverse
When the sword on the Enchiridion is turned sideways, it displays a holographic map of the known dimensions of the multiverse, as well as the connections between them. In it, each dimension is represented by a unique three-dimensional shape. Whether these shapes are true reflections of the dimensions or just symbols to help distinguish between them is unclear, although the depiction of the Time Room on the map is very similar to the depiction of the actual Time Room in "Finn the Human" and "Jake the Dog."

"Home" dimension
Described by Booko as "the universe in which we currently reside," this dimension is presumably where the entire series takes place. However, since Booko's speech is so brief and cursory, it is unclear whether special locations, such as the Crystal Dimension, the Dead Worlds, Lumpy Space, and the Nightosphere are considered part of or separate from the home dimension. On the multiverse map, it is visualized as a sphere inscribed within a spinning cube.

The Time Room

 * Main article: Time Room

Said to lay at the center of the multiverse, the Time Room is a special dimension which exists outside of time and generates the so-called "time waves" that all other dimensions experience as the passage of time. In "The Lich," Booko refers to it as the dwelling place of a being known only as "the almighty Prismo." It is subsequently revealed in "Finn the Human" and "Jake the Dog" that Prismo is actually the one responsible for the time waves; he even refers to the dimension as "his" Time Room.

Because it is described as a "quasi-corporeal," "single dimension," it is possible that the Time Room has no real physical existence and that its appearance in "Finn the Human" and "Jake the Dog" is merely either Finn and Jake's conception of it or Prismo's presentation of it. On the multiverse map, it is visualized as a cube with smaller cube-shaped voids in the centers of its faces.

Artifacts linking dimensions
When Booko describes the connections between the dimensions, he mentions that connections can be formed artificially by "artifacts of great power."

The Enchiridion
When the jewels from the crowns of all the princesses of Ooo (and the Ice King) are placed in the Enchiridion, it gains the ability to open a portal to any dimension in the multiverse. However, it seems that this power can only be used once: in "The Lich," Finn inadvertently creates such a portal when he tries to destroy the Enchiridion and prevent the Lich from obtaining it. After the portal closes, the jewels reappear but the Enchiridion seems to have been permanently destroyed.

It is unclear why the portal Finn opened led to the Time Room, the exact place the Lich was trying to get to. It is possible that the portal merely led to the space in between all of the dimensions and the Lich could have chosen, hypothetically, to go to any dimension he wanted to.