A bridge between Realms
"In theory, those who master Aura are able to bend the Existence on its knees. One of the possibilities is changing the properties of space, creating gates to other places."
Aura magic has the widest range of utility among all the elements, being able to bend even space and time. Among its spells, there is the creation of the Realm Gates, portals that link two Realms together, allowing one to traverse freely between them. During the Realm Wars, both Caeles and Mors made use of the Realm Gates to try and conquer Aequus, and they once devised together the technology to do so eons ago.
A Realm Gate bends the space around two realms, pushing them and bringing them together until they touch each other. Once this happens, anyone can cross to the other side and switch realms.
With the bending of the space fabric, the area surrounding the portal that is being created effectively "moves closer" to the other realm, which causes it to warp and take a shape resembling that of the realm on the other side. A more common example is how, in Aequus, the area around the Gate becomes dead, hot, and arid when it is connected to Mors.