I just came up with this idea, and i would like your opinion on this.
the planet was originally an eartlike planet, but about half the size.
Due an occurance (the impact of a meteorite of moonstone )it is now turning slow on its own axis, half of the planet is continual lighted and the other half is continual dark.
it didnt completely stop turning arround its own axis, but turns very slow...
It moves about 5000 meters per year. To complete a full turn will take about 3600 years.
If you build a city in the center of the light part of the planet , it will be on the dark site 900 years later.
Over the centuries the dark site became so cold because of the darknes and lack of sun that an ice-cap evolved. The dark site is now completely covered with ice.
The planet is moving very slow, so the city I was just talking about will eventually not only be on the dark site, but ALSO be covered under the icecap.
Many ancient cities have been swallowed by the ice and are ofcourse partially(the ruins) inhabited by the creatures that live on the icy/dark site.
centuries later the covered cities will pop up again on the other site, where the creatures of the light will move in again, build upon the ruins again etc etc etc,
maybe they have forgotten a city was ever build on the place , so it could be that 3 cities lie on top of eachother without someone knowing.... ofcourse mystery awakes
lots of plot possibilities 
Imagine living in a city that is coming near dark side of the planet. What do they do? Abandon the city?
Resist the cold and the evil of the dark side? Maybe some try... but all fail.
And when a city comes from the dark side to the light side, maybe full of treasures and ruins, I can almost imagine bands of adventurers running like vultures looking for the reamains. And weird monsters can still dwell there.
If the city took many years to cross the dark side, then the people on the light side may have forgot about it - or think that some specific city was just a myth that never existed.
The cities, in that world - and that is fascinating - are like living creatures: they will eventually die.
That is spooky for a city. They grow and get more rich every year... but they are also one year nearer death.
I have even though about the magic system.
I was thinking of about 4 moons or so, each moon representing an God.
Priests/clerics draw their divine power from the moon, when the moon is on the other site of the planet the power of these clerics weaken.
wizards/sorcerers also draw power from these moons since they are filled with somekind of magic.
the 5 moons are all on a different distance to the planet. so what i was thinking about is the closest moon replresents the low level spells, the one the most far away represents the high level spells.
actually wizards/sorcerers draw their magic from moonrocks. due to meteorites hitting the moons, rock from the moons has been slingshot to the planet. Because of the BIG meteorite of moonrock that hit the planet, from the moon that is the closest is that moonrock most commonly found on the planet. you NEED pieces of the rock as a spell component in order to cast a spell. NO ROCK = NO SPELL
the planet was originally an eartlike planet, but about half the size.
Due an occurance (the impact of a meteorite of moonstone )it is now turning slow on its own axis, half of the planet is continual lighted and the other half is continual dark.
it didnt completely stop turning arround its own axis, but turns very slow...
It moves about 5000 meters per year. To complete a full turn will take about 3600 years.
If you build a city in the center of the light part of the planet , it will be on the dark site 900 years later.
Over the centuries the dark site became so cold because of the darknes and lack of sun that an ice-cap evolved. The dark site is now completely covered with ice.
The planet is moving very slow, so the city I was just talking about will eventually not only be on the dark site, but ALSO be covered under the icecap.
Many ancient cities have been swallowed by the ice and are ofcourse partially(the ruins) inhabited by the creatures that live on the icy/dark site.
centuries later the covered cities will pop up again on the other site, where the creatures of the light will move in again, build upon the ruins again etc etc etc,
maybe they have forgotten a city was ever build on the place , so it could be that 3 cities lie on top of eachother without someone knowing.... ofcourse mystery awakes


Imagine living in a city that is coming near dark side of the planet. What do they do? Abandon the city?
Resist the cold and the evil of the dark side? Maybe some try... but all fail.
And when a city comes from the dark side to the light side, maybe full of treasures and ruins, I can almost imagine bands of adventurers running like vultures looking for the reamains. And weird monsters can still dwell there.
If the city took many years to cross the dark side, then the people on the light side may have forgot about it - or think that some specific city was just a myth that never existed.
The cities, in that world - and that is fascinating - are like living creatures: they will eventually die.
That is spooky for a city. They grow and get more rich every year... but they are also one year nearer death.
I have even though about the magic system.
I was thinking of about 4 moons or so, each moon representing an God.
Priests/clerics draw their divine power from the moon, when the moon is on the other site of the planet the power of these clerics weaken.
wizards/sorcerers also draw power from these moons since they are filled with somekind of magic.
the 5 moons are all on a different distance to the planet. so what i was thinking about is the closest moon replresents the low level spells, the one the most far away represents the high level spells.
actually wizards/sorcerers draw their magic from moonrocks. due to meteorites hitting the moons, rock from the moons has been slingshot to the planet. Because of the BIG meteorite of moonrock that hit the planet, from the moon that is the closest is that moonrock most commonly found on the planet. you NEED pieces of the rock as a spell component in order to cast a spell. NO ROCK = NO SPELL