Cythion of the Forgotten Ways

In any of the great temples, you will hear chanted recitations of the names of the gods, the saints, and the deeds. In the corners of the dark ways, you will find shrines to many of the Old. But in none of them will you see mention of Cythion of the Forgotten Ways.
In fact, unlike most deities, Cythion's influence does not come from worship, sacrifice, adoration or even simple acknowledgment of their existence. Nor does it come from people's belief in their power or request for favor. Cythion is unique; their influence exists because people don't consciously know of them. It comes from people's fundamental knowledge that there are mysteries that can not be understood or controlled. And when someone is under Cythion's influence, they never invoke them; at most, they feel confusion, fear or curiosity at whatever situation they find themselves in. They attribute the situation to their own failings to notice what is around them, or pride themselves in finding something that others had missed.
This influence is most often felt by the weary traveler who walks along a long and lonely road. The traveler takes no turns, and perhaps no other routes exist, but they find themselves somewhere unfamiliar, and in retracing their steps, only become more lost. Sometimes in their confusion, they find an object they weren't looking for. Sometimes they're offered a one-time opportunity to see something that hasn't been seen in generations. Other times, they may be the first people to walk a shortcut between two points. And sometimes, they simply find that they are nowhere, with no recognized path forward or back, and must complete some unknown task before familiar sites are revealed to them again.
Cythion seems arbitrary in their interactions with people. A well-traveled road might connect two locations a day or two apart. And then one day, a stranger or known and respected traveler might enter a tavern, talking of a village, a cottage, a non-existent bad turn they took along the road. They will describe scenes with convincing detail, of places and people that don't exist. Very occasionally, they describe something that did exist, but hasn't been seen in the lives of anybody present.

Historical Basis

It is not clear if Cythion is alive or dead, or in fact if Cythion ever existed as an old god. But because people truly believe in the mysteries of the lost traveller or found secret on a road, their influence exists as if they were both real and alive today.
The only modern hints to an answer are stories of someone drinking in a tavern with a stranger. They leave too intoxicated to walk, but find themselves at home without remembering the walk. Or they will offend the stranger, and find themselves on the wrong side of town, when their house is a few hundred feet away.
The stories may be hyperbole, the influence of drink, pranks or petty magics. But some people who find themselves lost or found describe the feeling of the stranger's firm hand on their back as they walked out of the tavern...and how they felt that hand until they arrived at their destination.

Variations & Mutation

The most pronounced variation of the deity is that there is no indication that their name is actually Cythion. Cythion is a corruption of an ancient word, cythcia, which refers to vivid but confusing dreams: Cythciat refers to a fever dream, while cythcini refers to the disjoined thoughts one has in between waking and sleeping. As a name, Cythion means "commander (or champion) of confused dream thinking".
The second variation is a difference of opinion as to whether or not Cythion can be invoked in some way. Nobody calls out to them directly, but some explorers who seek hidden ways will leave offerings at the shrines of old gods, hoping for revelation. Some invoke them as Yukathi ("Vision through always open eyes") or Descheyciel ("Lucky footfall")
Someone who is hiding, especially when there is only one place they could be, will sometimes pray that their location be kept hidden. A child running into a barn to hide from bandits might wish that the bandits overlook them, or they might pray that the bandits will not find them interesting enough to pursue. But some might hope that the bandits get lost between the house and the barn: take a wrong turn or find the path past the barn more interesting than the path into the barn. This last is an invocation of Cythion, however unintentionally.

In Literature

The most common stories that likely involve Cythion are those of people who find a secret location as they travel a well-known road. At that location, they find people, secrets or treasures. When they depart, wake up, stumble away, or otherwise return to their planned path, they are inevitably obsessed with returning to that place, to find a particular person, obtain more of the wealth they found, learn the last piece of a puzzle that wasn't fully solved or simply bring others to show that they did not imagine it.
Sometimes, the characters have objects that prove that they were somewhere else. Other times, they carry objects that are proof to them, but not to others. Sometimes, they have no proof, other than their words.
The stories vary, but can involve retracing the path, speaking to wizards, sages and storytellers for any evidence, advice or even just confirmation that what they saw has been seen before. Some stories talk of people who spend their fortunes in vain. Other stories describe people who found that the experience can't be repeated, but that their journey to pursue the truth provided its own value. In a very few stories, people wake up from a wild dream, and find themselves holding something that completes their search. In some tales that completion comes in time to solve a problem; other times it doesn't. In some tales, it drives the person mad to have their story confirmed in their own eyes, but not able to confirm it to others.
As a whole, this genre is referred to as "Dream Path" stories.

In Art

Most "Dream Path" art tends to the silly, and is much more prevalent than recorded stories that could be attributed to the influence of an old god. It's not that uncommon to get lost on a path one knows well, or to notice something on a path that hadn't been noticed before.
Therefore, art tends to show people foolishly ignoring what they know, and taking a wrong turn. Attractive women drawing a man's eye from their path, new shortcuts with obvious problems along it, and people sleepwalking past a turn they were supposed to take are all common and popular images.
Along the more mystical, some works show gremlins holding up shrubs or drawings that make it appear that a road doesn't exist. Such works imply that the traveler is easily fooled, as those things are never portrayed as a convincing trick.
In other works, a road is shown overlaid with a spirit road, and the traveler is taking their first step along that spirit road. In a very few pieces, there is a figure "laying down" that spirit road to be taken. That is the closest that art gets to a depiction of Cythion.
There are also works that represent scenes from any of several "Dream Path" stories. However, the image of the "first wrong step" tends to be more generally popular, because people relate to the situation personally.
Beyond visual art, there is also a small wooden toy or token that travelers sometimes carry with them, which can either show a single "path", or can be twisted into two diverging paths. In some cases, people carry them in their "single path" form as a safety token. Some brave or foolhardy people twist the path in a "let the world do what it will" gesture. And sometimes, a person will put a twisted token in someone's gear, hoping that they'll be lost--though this form of hedge magic is generally frowned upon.