The Penrose: Sinews of the Multiverse

## Overview

You carefully pass through the portal into a massive chamber filled with gray stairs that web in every direction without care for gravity or reality. There’s an archway nearby and you decide to cautiously inch its way. Once you have passed through the archway, your center of gravity shifts. You fall back. It’s as if gravity changed when you entered. To you, it was a doorway, but to the other side, it was a hole in the floor. You couldn’t wrap your mind around it.
The Penrose is a disorienting place that twists and turns as it takes you to unexpected places all over the universe. It connects everything, and that means many unsettling realms full of alien structures and unfathomable creatures. It’s most often renowned for its role as the connective tissue between everything else (which is where it gets one of its hundreds of alternate names: The Sinews of the Multiverse) Not enough people take note of what’s in the Penrose itself, however. For what lurks deep inside gravity-defying stairs is just as fascinating as the Museum of Worms or the Court of Mouths.

The most obvious feature of the Penrose is the unique way that gravity works here: as a plane of stairs leading in every direction—north, east, down, right, up, sideways, backward, inside-out, etc.—the gravity follows the stair, wherever it leads. Some pockets of gravity have two or more stairways competing for it, which means that if you ever try to throw something in the Penrose, it’s impossible to know where it will end up. It could drop to a stair far away from you with no easy way to get there, it could get stuck hovering in place, or float upward to a ceiling that’s actually just the floor of another bridge.

The Penrose isn’t homogenous. The stairs lead to many unique and often horrifying areas. Such places are known as the pocket dimensions of the Penrose. Though many have been discovered, there are possibly hundreds of unseen areas left to be found. This is the reason that the Penrose is so alluring: it doesn’t just act as a crossroad to other planes of existence. It also houses hundreds of small planes that cannot be accessed anywhere else.

### The dimensions of forbidden knowledge

The Penrose is a place full of unanswered questions. It’s almost as if the plane is alive, but it only uses its sentience to shroud its true nature. It actively attempts to keep its secrets hidden and stops those who enter it from asking questions. That hasn’t stopped a brave minority from denying the Penrose’s wishes. Penrologists, as they call themselves, focus research on answering unknowable questions. That’s their own description: they answer unanswerable truths.

Though the Penrose wants to keep itself a secret, penrologists have nonetheless uncovered many facts about it. Some of them are simple: like its anomalous gravity or its strange inhabitants. Others, however, were more difficult to unearth. Locked away in the Penrose are at least dozens of small pocket dimensions that function as their own microscopic planes of existence. Places such as the Untethered Sands or the Glass Steps. Many penrologists have died in the effort to learn more about these places. There are likely dozens of undiscovered pocket dimensions—perhaps even thousands.

One fascinating effect of the Penrose is that it saps away energy: both physical strength and mental fortitude. The longer you're within its sphere of influence, the more tired you'll be. That works to the plane's advantage. It's more difficult to remember the truths of the Penrose if you're constantly drowsy. Surprisingly, the most common way to die on the steps isn't from horrific beasts or lethal environments. It's from exhaustion. Those who have experienced the Penrose describe it as a cloud over their minds. They can't think clearly, and they become forgetful. Neglectful. Apathetic.

## Survival

There's no weather in the Penrose. Perhaps time doesn't even pass within its boundaries. After all, every visitor soon learns an unfortunate truth: you cannot sleep in the Penrose, no matter how much you might want to. What's worse, traveling the mind-bending landscapes is exhausting to the mind. The repetition of the paths contributes to this. Wherever you are, it will always dimly lit. You will always be surrounded by stairs made of bright gray bricks. It will always be intensely silent.

Because the Penrose is so tightly packed with serpentine, meandering pathways, it's easy to feel claustrophobic. Most of the time the only thing you can see is layers upon layers of more stairs in front of you. Maybe the featureless, repeating nature is by design: it makes it even more difficult to navigate and it makes you even drearier.

As dangerous as the creatures in the Penrose are, the biggest danger is the fight against exhaustion. Over time, explorers lose concentration, develop terrible headaches, act paranoid, and begin to hallucinate. In the Penrose, you can close your eyes, but you can’t rest. You remain conscious for every agonizing second. Until you can take it no longer, and collapse. In the Penrose, you can’t rest. When you collapse, that means you’re dead.

## Locations

The Penrose is more than just stairs. There are many portals to the other planes of the multiverse. The labyrinth also holds many small pocket dimensions that are unique to the Penrose and each is mysterious in their own ways. Penrologists spend most of their efforts trying to unravel the bizarreries of these small realms. They believe that the Penrose is many times larger than what they’ve seen, so research is ongoing into just how many pocket dimensions there are. These are the most prominent and well-known pocket dimensions:

* **The Museum of Worms:** A single room full of bookshelves containing dead bodies in various forms of decay from taxidermy to crumbling bones. Worms and maggots pervade the entirety of this place, and some of them are much larger than normal. The biggest one is the width of a tree trunk.
* **The Court of Mouths:** A cylindrical room with walls made of swollen gums and grimy mouths. They are a panel of judges as well as enthusiasts of oral tradition over the written word. The Mouths even conduct their own type of magic based around tattoos.
* **The Untethered Sands:** An endless maelstrom of sand where there is no gravity. The extreme winds carry more than just sand, however, larger stones and boulders also fly through the realm. Some of the boulders are the size of mountains and have ancient ruins carved into them.
* **The Glass Steps:** Imperceptible steps of crystal that lead to an unknown precipice. Below it is an abyss that glows intensely bright. A creature follows you as you ascend, whispering thoughts of doubt as you prove your worthiness.
* **The Gallimaufry:** The landfill of the multiverse. All extradimensional spaces—like Bags of Holding or Heyward’s Handy Haversacks—end up here. Everything here is marked with a mysterious symbol and a number that can be read in any language.
* **The Accrescent Farm:** A botanical garden that contains every plant and fungus that exists in the entire multiverse. Not just the material plane, but all the Outer Planes, Inner Planes, and beyond the Far Realms.
* **The Xanthic Forge:** A blacksmith where the weapons work by themselves. The center of the forge is a pool of lava that glows a brilliant gold. The smithies here make a unique material. It goes by many names, such as “Giltflesh” or “Auriferous Gold.”
* **The Subnivean Fortress:** A fortress of black bricks that is suspended in time. Everything here is frozen, including the inhabitants that have died from hypothermia within its walls. The Fortress does not like change. Do not move anything within the Fortress.
* **The Cracked Door:** The place where all the thousands of one-way portals to the Penrose lead. The passages around the Cracked Door are especially dangerous, as they’re filled with monsters that have seeped in from thousands of planes of existence.
* **The Library of Lives Future and Past:** The Librarian here is only interested in one kind of information: the biographies of those who have passed through his building. In this timeless place, that means there’s a book on every traveler that has visited him. As well as people who haven’t visited yet.

## Denizens of the stairs

Have you ever asked yourself who lives in the Penrose? A majority have not. After all: it’s easy to assume that the empty steps of the Penrose are universal throughout the entire plane. That’s not entirely accurate, though. It’s true that a vast amount of the plane doesn’t have any indigenous occupants, but that’s only the majority. In the Penrose, the center of the plane is also its four corners. Each of the corners is, in fact, an island that cannot be found without the knowledge of its location. The corners do not touch—nor can they touch, for they are the corners. Where the four islands meet, however, according to legend and to penrologist, the manikins reside. Faceless, featureless humanoids that don’t speak or eat. They wander the Penrose with their own hidden motives: shrouded in a heavy fog of questions, just as the plane they call their home.

Rarely do the manikins attack visitors to the plane, but there have been many exceptions to the rule. Most of the time the manikins are safe so long as they are unprovoked. Even that isn’t guaranteed. There are stories of people who were simply standing in the direct path of a manikin, only to be swiftly killed by the manikin as it continued its walk. When they do attack, they don’t attack the physical body, but rather the mind and the soul. They exhaust the mind until it can no longer function, slowly inching its victim closer to paralysis—then death. Their touch has more immediate effects as well, beyond sapping life-force. A weak-willed individual will succumb to temporary madness upon an attack from the manikins. The especially weak-willed may never recover from the madness they have been afflicted.

Manikins don't have traditional stats, because they can't be killed. They have no HP and an AC of 15. Instead of hit points, it takes 8 hits before they're chopped up enough that they're no longer a threat. When they've been hit 4 or more times, they attack with disadvantage. When attacking, they have a +8 to hit. With each hit, they inflict one level of exhaustion. In addition, the target must make a DC17 Wisdom Saving Throw or contract a short-term illness. If they fail by 5 or more, then it becomes a long-term illness instead.
The Sun Thralls are just that: servants of the Sun during its full glory. They can be glimpsed through nooks and holes in the veins of the Penrose. Just a glance of the horrific visage of a carapaced mass with unnatural, lanky limbs tipped with teeth or claw is enough to paralyze the most courageous penrologists. Now that the Sun is dead, the Sun Thralls remain in the Penrose and continue to enact the will of their late master: to recover as many objects, magic, and people as possible and to bring them back to the Coruscant Sanctorum. (the rumored lair of the Sun.) Some penrologists think that the behavior of the Sun Thralls didn’t start until after the Sun had met its end. If that is the case, then perhaps they are gathering these materials to prepare for the Sun’s revival?

Sun Thralls are just Chulls with a slightly different description and behavior.
Occasionally, students of the Court of Mouths slither their way onto the stairs of the Penrose. Heaping piles of swollen flesh, the students learn secrets from their masters but pay a terrible price. The slimy puddles of red are blanketed in rancid mouths with grimy teeth and tongues filled with muck. The teeth are carved and the tongues are tattooed with arcane symbols. They whisper the secrets of the Courts and try to convert more students.

Students of the Court of Mouths are repurposed Gibbering Mouthers with some innate spellcasting. Spells like Crown of Madness, Fear, Hellish Rebuke, and Tasha's Hideous Laughter all work well for this. I also give them Whispers of Madness and Howling Babble from the Allip statblock in Mordenkainen's Tome of Foes.
Skulks also lurk the halls of the Penrose. Invisible spirits long dead that are nothing but the shells of a former person. They want nothing more than to feel warmth again. Silently, they stalk visitors in the Penrose and await an opportunity to attack the hosts and steal their bodies. They are attracted to light because it reminds them of the warmth they felt in life. When a skulk has successfully overtaken a host, they continue to act as they did as a skulk. Though they feel warmth again, they cannot taste food or see colors. They live short, unfulfilled lives until they invariably die of thirst or starvation.

Skulks in the Penrose function similarly to their base statblock in Mordenkainen's Tome of Foes. Except I give them an action similar to the Will-o'-Wisp's Consume Life. Wherein the skulk takes over the corpse instead of regaining health. Essentially becoming an apathetic zombie.
## Travel

Since the Penrose connects everything, entrances can be anywhere. They can be as innocuous as a hollow tree stump or as grand as ornate doors in a temple. There are two types of entrances, however: static and dynamic

Static entrances remain the same for long periods of time or indefinitely. They’re dependable because they aren’t unstable enough to close while you’re inside the Penrose. Static entrances are highly sought after by penrologists, spellcasters, and villains because they allow an easy method of entering the Penrose multiple times. That includes both sides: it also offers a trustworthy way out of the Penrose.

Dynamic entrances are far fickler. They appear and disappear on a whim, so it’s impossible to track them down. Oftentimes, it’s impossible to know where a dynamic portal leads until after you’ve entered the Penrose. What’s worse is that all dynamic entrances lead to the same place: The Cracked Door. Since there are perhaps millions of portals scattered over the multiverse, the Cracked Door is a very dangerous area where you could meet extremely powerful creatures. Worst of all: The Cracked Door is a one-way portal. Once you’re in the Penrose, you’re trapped until you can find another exit.

Since the entirety of the Penrose is just endless steps, it can get boring if navigation is a constant routine of navigation checks and encounters. To fix this, I always describe a set of pathways (which I always call threads) described by one of the five senses. All these pathways call to the players and take them to different areas. Either the pocket dimensions, a proper plane from the cosmology, or an exit to the prime material. Examples of descriptions I’ve used in the past:
* A frigid breeze that chills you to the bone
* Sand calmingly rolling down your body
* The vision a bright light refracting through glass shards
* The sweet smell of fresh flowers

Whether these descriptions lead to what one would expect or subvert expectations is entirely up to you. Generally, I like to hide the *thread* that leads to the exit behind an unexpected description. The Penrose tries to keep itself a secret, so it makes sense that it would also make leaving difficult.

So, in a plane of gravity-defying stairs, how do you navigate it in-game? Since the Penrose saps your mental strength and alertness, I choose to have players roll either a Wisdom or Intelligence check with a sliding DC. The DC is 2d12. If you’d prefer less danger, you could change it to 2d10 or a static number like 12 or 14. On a failed check, there are several things that can happen: There could be an encounter with one of the denizens of the stairs, the players could get trapped in an Endless Stairwell, or a level of exhaustion could be taken. I started by randomizing the outcomes, but I’ve defaulted to choosing whatever’s most dramatic or interesting. On a successful check, they get closer to their *thread* of choice.

## Mysteries of the stairs

### The Stairs That Do Not End

Every turn in the Penrose can lead to an unexpected place, but there is a set of places that you don’t want to go: The Endless Stairwells. On journeys in the Penrose, navigation is imperative to getting around. If you fail to master the lurching pathways of this knotted labyrinth, you will likely stumble into an Endless Stairwell. These places waste time, energy, and can sometimes lead to death. Exiting an Endless Stairwell takes a melding of the right acumen, practical skill, and luck to progress, but even if you succeed, there’s a price for your efforts. Like everything in the Penrose, the stairwell takes a toll on your mind and drains your body’s strength, leaving you weaker than when you entered. Repeat this process dozens of times, and it is evident why so many penrologists meet their end within such a vicious cycle.

To get out of an Endless Stairwell, I employ skill challenge in which any skill can be used if it’s well-justified. It only takes two successes to leave, but each failure results in the player that made the check taking one level of exhaustion. The DC for all checks is equal to 10+2d4. Feel free to use a set number if you would rather not roll every time the party encounters an Endless Stairwell.

### Combat in the penrose

Combat atop the stairs is the one thing that I have never been able to nail down. I can describe scenes of traversing the stairs that translate well to the mind’s eye, but every time I’ve tried to translate it to pen and paper it becomes difficult. Three-dimensional maps are difficult enough to represent on paper but add mystical teleportation and impossible shapes and it’s literally impossible. That’s not to say that I haven’t tried, but all my attempts have been lackluster.

My current solution to this is what I call a “hidden loop” map. It involves having color-coated pathways that link up to each other in a way that makes it feel like you’re twisting around in weird ways. The secret is that these maps are self-contained loops that you can’t actually get out of during combat. It’s not a great solution, but if you need to play with a grid then it’s the simplest option I’ve come up with. Here’s an example of a hidden loop map:

Theater of the mind is another option, but even then, you run into problems: how do you accurately convey what’s happening during fights while making it feel different from combat in a flat field? I rely heavily on description to do that, but that feels unsatisfying to me. I can tell you that you and your opponent are fighting each other with your swords raised above your heads because to you, your enemy is on the ceiling and vice versa. That may be a fun image, but I want there to be a mechanical difference to fighting in the Penrose. I haven’t found a way to accomplish it in a way that flows well with the game, unfortunately.