Portals between dimensions are often called rifts in the olden texts. In a technical sense, that’s all they are.

Before the current Waking World became as peaceful as it is now, rifts appeared at random all over the planet. V̵̳̮̇o̷̳̬͗i̵̖̺̍͝d̵̠̋̚ Dwellers were able to pass into the Waking World whenever they liked. On the other hand, most humans were unable to enter the V̸̤͔́̋́͑͛̌̒̕͝͝o̸̒̄̾̿̇̈́̿̒̈́̄͝͠i̸̢̛̤̜̟̅̽̾̓̿̓̕͘͘͝d̵̛̛̛̻̍́̓̏̒͋́̅̏͑̌̐̂͘ through these same rifts.

…Now, the conditions of usual rifts have flipped; those who possess Waking World souls may enter the V̵̳̮̇o̷̳̬͗i̵̖̺̍͝d̵̠̋̚ , but V̵̳̮̇o̷̳̬͗i̵̖̺̍͝d̵̠̋̚ Dwellers, who supposedly have no souls, cannot enter the Waking World. Rifts that transport any entity from the Waking World to the V̸̤͔́̋́͑͛̌̒̕͝͝o̸̒̄̾̿̇̈́̿̒̈́̄͝͠i̸̢̛̤̜̟̅̽̾̓̿̓̕͘͘͝d̵̛̛̛̻̍́̓̏̒͋́̅̏͑̌̐̂͘ must be summoned through special casts. It is worth noting that cryptids became far more prominent around the time base rift conditions changed.

…And it is also worth noting that spells exist to make rifts with different usage conditions… but even one rift that can be used by a V̸̤͔́̋́͑͛̌̒̕͝͝o̸̒̄̾̿̇̈́̿̒̈́̄͝͠i̸̢̛̤̜̟̅̽̾̓̿̓̕͘͘͝d̵̛̛̛̻̍́̓̏̒͋́̅̏͑̌̐̂͘ Dweller would be disastrous for the current Waking World.