Underworlds (Worlds Collide Supplement)
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About Worlds Collide
Dungeon Master's Guide
Underworld is a catch-all term for all demiplanes that exist "under" the nine worlds of the Material Plane.
Details concerning the Underdark can be found at Sword Coast Adventurer's Guide, page 99-101.
Those who were fortunate enough to return from the Realms Below has reported that they have seen worlds and planes that did not belong to any of the nine worlds. Although most of the eyewitnesses were too disturbed at the experience in the Underdark to be fully believed, their comments seem too convincing to be a hallucination or a nightmare.
Demiplanes, also known as pocket dimensions, are extradimensional worlds too small to become a proper plane of existence by itself. Although demiplanes often embody unique rules on their own, they cannot exist without clinging onto other worlds. Powerful wizards can create one's own demiplane with a certain spell, such as demiplane.
Many scholars have attempted to demonstrate the name of this particular demiplane in known languages in all nine worlds, but every atttempt ended in a failure. It turned out that only numerical and mathematical signs can barely outline the very existence of this world, hence the name agreed by mind of Zeitraum.
As usual, those brave and tough have volunteered to explore the land of 0x022E09. Of seventeen bold adventurers, only five has returned; and their stories, told in a voice cracked with horror and paranoia, tells the world of absolute law and rules. Everything, everything in 0x022E09, was a cog, a bolt, a nut, or a crank that composes the entirety of the great mechanism that is 0x022E09. In there, they were anomalies and errors, which have to be "fixed" in order to preserve the routine. Twelve were victimized from the "cleaning" process - and of five survivors, two of them suffered a great degree of mental strain, and one of them was hollowed from within, speaking in complete monotone and questioning the necessity of individuality and free will every 13.4 seconds, sharp.
Also known as the Garden-Manor, Al-Hadiquasur is the beautiful demiplane that belongs to a mighty entity known as Bal-Hadad.
The portal to Al-Hadiqasur can be found in Muhajayd and Nomimkal. Bal-Hadad is known to enjoy his small bowl of sherberted sweets after his meals, so it would be no wonder to stumble upon one of his handyman in the frigid tundra of Kaotischinye.
The enigmatic demiplane of Fhwtxyh-H'Tw is well known for its obscure nature. Yes, it's that kind of demiplane.
Studies on nine worlds, overworlds, and underworlds have been conducted in all corners of the nine worlds, especially after the Worlds Collide incident. Most of what is known of overworlds and underworlds are observed, recorded, and even explored during the past fifty years. There were only three studies on Fhwtxyh-H'Tw so far, and none of the research results speak of the same thing. It is very, very safe to say that the only thing that is known of Fhwtxyh-H'Tw is that nothing is known of this realm.
Nothing is absolute in Fhwtxyh-H'Tw, and no observable rule is available in there. The only thing predictable in Fhwtxyh-H'Tu is that whatever you imagine, it will be even stranger and unpredictable in this chaotic, ever-changing demiplane.
Adventurers often describe the mind-boggling experience they had in a strange land, where all four corners of the world were blindingly white, and the only comfor to the eyes were hung up in the sky, in the shape of pitch-black sun. Through the flashing landscape they could make out the glimpses of doors and gateways, located in random direction and location. The story often ends with the teller grabbing one of the doorknob in random - which lead to exactly where they are now.
Also known as the Gate Dimension, Pordegurb is a demiplane full of doors and gateways. Scholars speculate the Pordegurb is the medium dimension for all teleportation and world-crossing portals, but they could not make the testimony for their hypothesis. Many attempts, especially from the Questus Empire, has made to utilize the demiplanes as a means of transportation, but such attempts have failed, mostly because of the random nature of Pordegurb, but also because they often ended up in somewhere they could not survive for more than three seconds.
Gateway from Pordegurb can be found in all nine worlds of the Material Planes, and some other demiplanes as well for that matter, but all known reports of gateways to Pordegurb were from Neutrala