A Thin Veil
Not much separates the world of Tessam from the fey realms. The veil between the planes could open anywhere. A child running underneath a toppled tree, a shepherd chasing after her suddenly uncontrollable dog, a servant tripping in a staircase. Suddenly they find themselves in another place. It won’t be obvious at first. Minor details might be off, but they would simply brush that off as a faulty memory. Perhaps the lighting has changed a bit, though that could just be their imagination. But as the child walks a little further, the air suddenly gets colder and when they turn around the way home is nowhere to be seen. The shepherd is unable to find the dog until it bursts out of the bushes, teeth bared and thorns growing out of its fur. The servant hurries to catch up with his friends, but the castle is slowly turning into a maze before his very eyes.
The fey realms dont obey the laws of the natural world. Leaving your backpack next to you on the ground doesn’t guarantee that it will be there when you turn back. There isn’t even a guarantee the ground will remain solid for long. But one has to travel far into the outer realms for things to get that wild. A short foray into the few isn’t nearly that dangerous. So long as one realizes what has happened and manages to retrace the path that led into the other plane, it is rather trivial to get back to the real world. One simply has to pay attention. Which is to say most people who accidentally stumble out of the world are never seen again. And those that do return are forever changed.
Time in the Fey
Travelers who return from a journey into the fey realms give wildly different reports on how long they have been there and what they have seen. It is hard to ascertain the truth of what places they went, but it is a widely accepted fact that time flows differently on the other side of the veil.
What Used to Be
Noone can claim to truly know what the fey realms are. But the prevailing theory is that they are echoes of the pre-cataclysmic world. This theory is supported by the few encounters mortals have had with intelligent fey life, such as hags and fairies. However, there haven’t been many of those as the only creatures that seem eager to approach mortals are mindless beasts looking for a meal.
However, those few fey who do agree to have a chat with mortals all have conflicting opinions on what the fey realms actually are. Scholars studying the planes have agreed that there must therefore be several parts of the fey realms, all with different properties and inhabitants. Some might not even be aware of the others based on what witnesses say. As of now, the known realms are The Feywild, The Abyss, The Fields of Fear and The Broken Peaks.