Portal

A portal is a type of anomaly that exists as a space-time transition between true reality and the Other. Portals come in an assortment of types, ranging from hard-surface portals such as walls and floors to open-surface portals such as the underside of tree branches. It is unknown as to how or why these portals form between true reality and dimensions of the Otherworld, but it is presumed that at least some are thanks to the broaching of entities into our world and the maintenance of a "doorway".

Origins
The origins of portals are almost entirely unknown - with the exception of a scant few hypothesized to be used by entities in transitioning between the Other and true reality. Those that do not come about by an intelligence such as an entity are random in their appearance, properties, and linked location, and often prove traumatic or outright fatal to humans that cross them without realizing what has occurred.

Scientifically, it has been ascertained that portals are a result of some sort of space-time interaction between true reality and the dimension of the Other that it comes into a "transdimensional" contact with. This interaction leads to the opening of a physical channel that may or may not violate the laws of physics of true reality.

Hard-surface portals
The term hard-surface portals refers to portals that come into being as a facet of some hard object, such as a wall, closed door, or floor. Those that come into contact with the supposedly rigid surfaces of these objects will instead have their extremities - or their body entirely - phase out of true reality and seamlessly enter into the Other. Due to the closed features of the objects, those that transition to the Other from hard-surface portals will almost always be attentive of the situation as they see their limbs or entire bodies shift into something that should not be "open".

Open surface portals
Open surface portals are portals that do not "inhabit" a hard, rigid surface such as a floor or wall, but instead exist somewhere within open air. This can include anything from a doorway or the underside of tree branches to a random open-air spot in the middle of a field. These portals are considered to be the more dangerous of the two types, as individuals who cross these portals have a chance to not realize that they have entered the Other for extended periods of time.