Liminalities
Liminalities have a few rules:
Time and space work differently. In space, Liminalities abut the world at distinct points, usually doors, nooks, alleys, and other folds. Within are perforated spaces where any node may (but not must) connect with any other. Time in a Liminality flows faster or slower. It may be possible to use one to travel back in time, but no one really knows.
Liminalities permute ‘imprints’ of where they make contact with the world. Open a strange door in the sewers and find yourself in a maze of pipes, sluices, and tunnels. Through the hollow log in the woods is an endless gloaming thicket. People, feelings, and ideas can all be imprints.
The walls are thin; behind them: empty space, churning machinery, roaring water, clouds, and heat.
Liminalities respond to humans. Where there are light and order and crowds they withdraw; where there is murk and silence and solitude they beckon. Visitors say intelligence pervades them the way it does an ancient tree or a river. Some say their power is growing.
Cats, owls, moths, snakes, salamanders, certain fish, dragonflies, deer, toads, crows, monkeys, octopi and select other creatures are known to frequent liminalities. Most animals avoid them.
Terrible monsters lurk in the Liminalities, as do unlikely friends. Most are indifferent, all are dangerous.
Liminalities subtly alter those who explore them.
Liminalities are my spin on a very old idea: the mythic underworld, faerie, the backrooms. They are also my version of D&D’s planes, inasmuch as they can answer questions like ‘where to demons/fey come from?’ and ‘how did that ogre find its way to this room?’. It may be that they are an ancient form of genuine magic, or it may be that they an old and decaying technology, perhaps used for travel, punishment, or art. In any case, they’re where I’ll slot in depthcrawl modules like Gardens of Ynn and The Stygian Library.