Ysoma

Ysoma
Ysoma is one of the Twelve Moons of the World.  It is one of the Open Moons and is often referred to as the Green Moon of Memory.  Travel to Ysoma is difficult; direct terrestrial access can only be granted from the Moongate in the city of Ring.  Many travelers prefer the safer, but costlier method, of buying passage on a moonbound craft from Astropolis.
The surface of Ysoma is covered by a green lichenous growth, quite thick in some places.  It is this lichen that gives the moon its distinct color and is believed to play a part in producing its breathable atmosphere.  However, prolonged inhalation of the lichen spores is dangerous and can lead to an illness known as Green Moon Fever.  Green Moon Fever is characterized by hallucinations, an increased sense of paranoia, increased agression, nausea, vomiting and, sometimes, convulsions.
Because of Green Moon Fever no one can remain on Ysoma for longer than 24 days without succumbing.
Littering the surface of Ysoma are structures known as memory castles.

It is speculated that in the Old World, Ysoma was used as an archival site.  These memory castles are vast data storage devices, containing a multitude of valuable information.  They attract hundreds of people to Ysoma, hoping to access their secrets and walk away with some valuable slice of data. Successfully penetrating a memory castle and attempting to access its secrets is extremely dangerous. The internal layout of the structures can change, trapping a party in an everchanging maze or, worse, crushing someone to death between moving walls.  There is an entire specialist trade built around penetrating the memory castles. These people are generally referred to as memory breakers.

There is only one quasi-permanent settlement on Ysoma.

Green Moon Village was established by the first wave of colonists, before anyone knew about green moon fever.  After their first month on Ysoma, the village descended into madness and violence. Only a handful of the original colonists survived and most of them never returned to Ysoma.

Today, Green Moon Village acts as a base for memory breakers, sightseers and other travelers to Ysoma.  The only permanent residents are a handful of mechanicals, who manage most of the business establishments.