Ryloth, also known as Twi'lek, and Twi'lek Prime, was the harsh, rocky homeworld of the Twi'leks, an Outer Rim Territories world located on the Corellian Run and forming one endpoint of the Death Wind Corridor. One side of the planet perpetually faced its sun and the other remained in darkness, a phenomenon known as tidal locking. The dayside was referred to as the Bright Lands and the night-side was known as the Nightlands.
Ryloth, the second planet in the Ryloth system, possessed a thin, but breathable atmosphere. The planet was orbited by five moons, which had subtle tidal effects on the planet's liquid core and underground springs. It had little or no surface water except for patches of water ice on the night side.
It was a planet of extremes: dry, rocky landscapes of deserts, mountain ranges with mist-covered peaks, shadowy valleys, alternated with snowy wastes, joined by lush temperate bands which concentrated much of its population.
Because of its unusual day-night rotation period, atmospheric conditions on Ryloth's surface were characterized by turbulent seasons and extremely high winds (reaching 500 kilometers per hour) scouring the surface and sculpting the landscape and unpredictable bursts of heat called heat storms, which could reach 300 degrees Celsius. The more extreme heat storms sometimes moved across the terminator and reached miles underground, making caves near the surface temporarily uninhabitable, before eventually dying out on the night side.
Along the terminator lay a thin habitable border, a twilight realm between the two extremes. Along this narrow strip were the series of caverns where some of the Twi'leks decided to build their underground cities, blockaded with thick blast doors and portcullises to keep out the vicious monsters that prowled the Bright Lands, especially lyleks.
The Floating Rock Gardens of Ryloth were a natural wonder and tourist attraction, well known throughout the Outer Rim, where strong winds blew among the tunnels, causing rocks to float gently through the air. Over the years the gardens became filled with rare and dazzling stones. Visitors were allowed to rearrange the stones to their liking, but were encouraged to seek meaning in the natural configurations.
Kala'uun was a permanent city located within the Lonely Five mountain range, boasting a large underground spaceport.
Ryloth was originally discovered by Old Republic explorers approximately 10,000 years before the onset of the Clone Wars and was one of the first worlds discovered in the Outer Rim. Located at one end of the Corellian Run, it was one of the few worlds of the galaxy further from the Galactic Core than Tatooine.
Civilization on Ryloth at the time of its discovery was not particularly advanced. Twi'leks integrated windmills and turbines to power their homes and industries carved out of the mountains. The cultivation of fungi and molds provided nourishment for the populace, as did the rearing of the domesticated herd animals rycrits for meat. Twi'leks never developed space travel, but instead expanded throughout the galaxy by trading with the Republic, variously negotiating, charming, or seducing their way to the stars.
The slave trade had been an everyday part of life on Ryloth for millennia and persisted long after its contact with the Republic sometime in 10,000 BBY. Dancing girls were especially prized, and as Twi'lek communities were established throughout the Republic and elsewhere, they found numerous eager markets. The slaves were often sold by 'contract,' as a feeble way of evading antislavery laws.
Female Twi'lek consorts and companions soon became a status symbol among the rich and the decadent throughout the Galactic Republic and eventually the Galactic Empire. The slave trade remained profitable all throughout Ryloth's history, and though the early slavers were Twi'leks, over the years many alien crime lords migrated to Ryloth for a piece of the action.
Twi'leks of all professions eventually became a common, even ubiquitous, sight all over the galaxy, as businesspeople, servants, bodyguards, majordomos and slaves. Their near-Human appearance made them less a target of anti-alien prejudice than others during the Imperial era.
The Anx crime lord Graxol Kelvyyn had his headquarters on Ryloth shortly before the onset of the Clone Wars. He was known for having a vast slave-trading network that covered the Outer Rim and even reached Kidiet Olgo in the Galactic Core.
Prominent examples of Twi'lek slaves during the last days of the Republic and the Empire included Ann Gella and Tann Gella, twins owned by Sebulba, and Oola, owned by Jabba the Hutt.