Transportation between the The Prime Material Plane and other planes is done via extraplanar portals. There are other methods, but portals are the most common. The true nature of portals varies wildly, especially depending on the linked plane, but typically they fall into a few categories. Note that the physical size of the portal is not at al a limiting factor in what can pass through it, only its tier. For example, a whale can pass through a Tier 4 portal, but a gnome cannot. For portals monitored and controlled by individuals, a common practice is to set up a doorway on the near side of the portal to control this as needed.
Tier 1
Tier 1 portals are tiny, often imperceptible without highly specialized magical detection equipment. Raw magical essence leaks out, but in small enough quantities that very little change occurs on the material plane. Given that these usually exist already in locations rich in a specific magical essence, they can go unnoticed for centuries. However, concentrated effort on either side of the Tier 1 portal can cause it to grow into a Tier 2 portal.
Tier 2
Tier 2 portals are always visible to the naked eye, and have noticeable effects on the landscape around them. For example, a Tier 2 portal to the Charred Dominion will cause things nearby it to spontaneously combust, intense heat can be felt even from several feet away, and shadows are greatly diminished. However, nothing can yet physically pass through the portal.
Tier 3
A portal is classified as a Tier 3 portal once it becomes large enough for inanimate objects to safely pass through. Often devils take advantage of these portals to distribute contracts, without letting the recipients knowing the true appearance of the writer. Nothing intelligent or imbued with magical essence, except an essence matching that of the portal, can pass through.
Tier 4
These portals allow unintelligent creatures to pass through. Animals, plants, magical objects, complex constructions, and golems can use this portal for transportation, but nothing more intelligent.
Tier 5
Tier 5 portals allow nearly all creatures and objects to pass through, excepting only gods and near-divine beings. They require long, complex rituals to create, and these procedures are vastly different between different planes and are even dependent on which sector of the plane the portal is connecting through. However, once established, these portals are very stable. Only specific rituals can close them; otherwise, they last indefinitely. There are still many undocumented Tier 5 portals throughout Eochora that have remained since the Elemental Era.