Dark alleys

Kundel ran with his client through the maze of streets and walkways. The enraged Spirit seemed to be closer and closer to them. They were still quite a distance away from their destination, and they didn't have much more time before they were caught. One of Kundel's dogs showed up and pointed to the side. At the narrow alley between two buildings. Kundel looked inside. The tunnel before him was pitch black. And not in an "it's really dark in here" way. More like the pure blackness, the kind that makes all hair on the back of one's neck to stand up and get covered with cold sweat.
Still, that was the only way to lose the Spirit.

Even before The Curtain fell, dark alleys were considered dangerous places. Ones to stay away far away from. And yet, once in a while, they were used as shortcuts between two places. The kind you almost run through without looking back. Because looking back could confirm your fears.
After the material and conceptual (spiritual) worlds merged together, dark alleys are still here. And they kept both their function and all of the negative emotions connected to them.

A short-distance shortcut

Out of all of the Shortcuts that showed up after The Curtain fell, dark alleys are one of the shortest. The longest ones tend to connect two points less than 0,5 km from each other. Additionally, dark alleys only show up if someone is in a dire situation, either being chased by something or time rushes them, so they usually only lead closer to one's destination or just out of reach of the thing that chased them.

Manifestation

Dark alleys take on a form of a narrow gap between two walls, barely wider than the shoulders of the one who will use it. Less than 1 meter inside, there is no light that reaches into it, no matter the weather conditions outside. No tools of human, natural, or spiritual origin can illuminate it. The walls of the alley are solid, however, any interaction with them creates ripples that spread through their surface.
Inside the alley, all of the senses seem to be dulled, and once there, it is impossible to perceive anything outside of it. One doesn't know if the place they ran away to is safer than the one they left. As such, the alleys are taken only by those who are desperate.

They had no choice. Kundel went in first.
As soon as his foot touched the darkness of the alley, almost all of the sounds stopped. Each step he made sounded like it came from somewhere deep, almost disorienting his senses. He didn't even know if his client was still there. He just moved. Step, after step.
He didn't know how far he traveled or how much time has passed, but at some point, he heard something.
"It's... beautiful," those words came from behind Kundel.
A few moments after he heard them, he finally left the alleyway. When he turned around, behind him was a solid wall.
He looked around. He was just one street from the closest settlement.

Type

Metaphysical, Supernatural

One rule

When entering the dark alley, there is only one rule.

"Look only in front of yourself. Don't turn your head. Don't look to the sides. And ignore the sounds and the ripples."

As long as one obeys that one rule, traversing the dark alley should come without any risks. Even touching the walls of the alley, a thing many people who enter it fear, as it creates ripples that spread all around them, is completely safe.

And if it is broken

Those who break the rule will see something beautiful. A glow, moving colors inside of the pure blackness of the alleyway. Some describe it as galaxies, others as deep-sea fish swimming around. Whatever they see, it doesn't matter, as the alleyway will consume them before they manage to leave it, though it sometimes gives them a few seconds, so their words may pique the curiosity of others inside its borders.
Once the alley eats someone, it will close or turn back into a normal alley (if it was one before) once everyone leaves its perimeter.
It doesn't matter if one can see the sides of the alleyway. Being blind or covering one's eyes doesn't protect from being consumed. The alley simply knows if someone broke its rule.