Being a planet that is tidally locked around its star, Ryloth finds one side of its surface constantly in day and the other side frozen in night. This tidal locking of the planet's rotation has caused its core to become malformed into an almost egg-like shape pointing towards the system star. This in turn affects the mantle by locking only dynamic magma and the plates in the planet's crust towards the edges of the planet where night and day meet.
The dynamic plate effect created a mountain ridge which, being on the boundary between night and day, is the only location habitable by unprotected humanoids. But even this region is full of dynamic weather, as the heat from the day and freezing air of the cold side of the planet meet, creating an almost constant hostile weather pattern.
Surprisingly enough, a sentient race came into its own on Ryloth, living within the mountain ranges in the temperate zone, somehow eking out an existence despite the lack of wildlife on the planet. Some of the galaxy's brilliant minds look at the Twi'lek race, the sentient race which hails from this world, coupled with the lack of diverse flora and fauna, and believe that once, long ago, Ryloth was a dynamically rotating world.
Indeed, in the magnetic north region of the world, there is not even a crust, just a constant bubbling of magma from deep in the planet where the core pushes out. It is assumed that this massive hole in the planet's surface being tidally locked dead centre towards the star does not explain itself without a massively traumatic incident. This, some believe, would have to be an impact from a comet that ripped Ryloth into a slightly further orbit, slowing down its period of rotation and ultimately resulting in a tidal lock.
But after thousands of years of Ryloth's civilized history, little evidence has been collected or analyzed. Its mountains, while having old strata, are from a deep source within the crust and do not have the telltale signs of complex life. There have been some who have brought back some artifacts from deep within the deserts and glaciers of Ryloth, but these artifacts are believed by most as being unreliable due to their sources. Overall, the danger level from the planet, its weather alone being known to knock starships out of the sky if their captains are not careful, in addition to having two hemispheres that quickly heat up and cool down and corrosive winds carrying sand or ice crystals, have prevented any real scientific study.
However, there is no escaping the fact that Ryloth has been a key planet within the galaxy. Its native sentient population has been in and out of galactic politics, by choice or by force, for tens of thousands of years. With the first finding of the drug Ryll on the planet, the planet found itself being exploited by outside forces. As a by-product, the Twi'lek species and its culture have been molded to fit both the hostile elements in which they live and the extra-solar exploitation of its people and natural resources.
Ryloth's capital city is Kala'uun, which is a tourist destination located within the planet's bisecting mountain range.