Lost City of the Jedi The Lost City of the Jedi was a secret city and terraforming station , located deep below the surface of the fourth moon of Yavin Prime . Thousands of years before the rise of the Galactic Empire , at the end of the Great Sith War , members of the Jedi Order chased the renegade Exar Kun to Yavin 4 . Wishing to obtain the demise of the Sith and bring the war to an end , the Jedi launched a salvo of destructive energy at the moon , trapping Kun ' s spirit in his temple but ravaging the surface of Yavin 4 in the process . This environmental catastrophe completely destroyed the ecosystem of Yavin 4 , and the Lost City of the Jedi was built to nurture the world back to health . History . The terraforming of Yavin 4 . Around 4000 BBY , a rogue Jedi apprentice named Exar Kun partnered with the Krath cult to form the Brotherhood of the Sith , in hopes of bringing down the Galactic Republic and the Jedi Order . Kun had been christened the new Dark Lord of the Sith by the ghost of Marka Ragnos , and had established his quarters on the fourth moon of Yavin Prime . The series of battles that ensued , known as the Great Sith War , resulted in millions of deaths . Four years later , Ulic Qel - Droma — a fallen Jedi and ally of Kun — betrayed the Dark Lord and revealed the secrets of Kun ’ s power base . Soon , a legion of Jedi , led to Yavin 4 by Qel - droma , arrived to stop Kun and bring the war to an end . Unyielding , Kun decided to drain the life of thousands of Massassi so he could trap his own spirit into the walls of a temple . Determined to end the war , the Jedi banded together and created a wall of light , a devastating salvo of light side energy , which they launched at the planet . This powerful combined attack accidentally ignited the moon ’ s jungles , causing the deaths of the few remaining Massassi , levelling most of the temples and razing the rain forests to the ground . Kun ’ s spirit had been trapped inside his own walls , but the ecosystem of Yavin 4 had been ravaged in the process . The Jedi Order sought to reverse the damage their wall of light had caused and established an underground terraforming station that would restore the moon to its former state . Following the fires , the landscape of the moon had become barren and cold , but a group of Jedi Masters discovered they could change the climate by creating a way to bring heat from the moon ' s core to the surface . This involved drilling deep shafts into Yavin 4 which were designed to release steam as well as heat into the atmosphere . This in turn led to the development of the Weather and Climate Command Center . Once established , the Center manipulated the moon ' s environmental conditions , which in turn , made the moon warmer and more tropical . Once this was done , the Jedi began seeding the four continents , thus allowing lush forests to grow again on Yavin 4 . Upon the completion of this terraforming process , the Jedi began to make arrangements for a subterranean city which , in time , would become known as the Lost City of the Jedi . The settlement was created on the moon ' s largest continent , and it was built deep underground , below the rainforest , in a huge cavern . Using deep shafts similar to the ones they cut to release the heat in the moon ' s core , they created tubular transports that allowed for travel between the underground city and " Topworld " — which was the name given to the surface . One method of entry was a round wall made of green marble which was located in the forest . Inside the underground cavern were numerous dome houses that housed Jedi Knights as well as various pieces of advanced equipment . Beyond its ecological importance , the new city also had the function to guarantee the spirit of Kun would never break free . From history to legend . At some point after the founding of the city , the organic inhabitants left , and an army of droids took over the care - taking of the settlement . The facility consisted of travel tubes , computer cubes as well as droids of every possible design . This high degree of automation meant that the city was highly busy due to its droid occupants who were always modifying the computers , making new droids or repairing old ones and doing other maintenance duties such as working on the power generators , cleaning as well as maintaining the hundred domes that dominated the city . In time , the city became forgotten and was considered nothing but a legend in the centuries that followed its creation . Nonetheless , the city remained active and its droid occupants would , on occasion , journey to the surface of the moon and gather information which was used to update the history of the galaxy for the Lost City ' s Jedi Library . Around the year 7 BBY , an unknown brown - robed Jedi Master brought Ken , the supposed grandson of Emperor Palpatine , to the city to keep him safe . For twelve years , the boy grew among the droids of the Lost City , away from the dangers of the dark side but in the ignorance about his origins . Following the Battle of Endor , the Bimm impersonator posing as the Supreme Prophet Kadann intended to get his hands on the ancient knowledge hidden in the Lost City . In order to find the location of the famed and forgotten city , the false Prophet abducted the young Prince Ken . He promised he would reveal the secrets of the boy ' s origins if he was told the correct geographical coordinates of the Lost City . Ken was troubled by this promise , and he gave the pseudo - Kadann the information he sought . The Jedi secrets contained in the city ' s master computer almost fell into the fake Prophet ' s hands , but the Grand Computer was destroyed by blaster fire , leaving Kadann and his minions inside the crumbling city . Although they eventually escaped , the city itself had been damaged enough that Exar Kun was now free to wander the entire moon . Design . The Lost City was built several miles below the surface , in a cavern lit up by bubble lights and fluorescent rocks . Most of the city ' s buildings , where the Jedi used to live , were dome - shaped . The city was criss - crossed by roads made of perfectly cut stone . Jedi Library . Within the Lost City of the Jedi was a great library which possessed records that dated back for thousands of years . The majority of the records were located within a master computer that possessed files placed in there by the Jedi . In addition to these electronic records , there were also ancient manuscripts as well as books . Inside this repository of knowledge was information of all civilizations and the history of all planets as well as moons that had intelligent life on them . Weather and Climate Command Center . The complex facility was developed by the Jedi thousands of years ago and placed within the Lost City . It consisted of a series of pipe shafts that tapped into the moon ' s core and brought heat as well as steam to the surface . This allowed a level of control over the weather patterns of the moon and allowed it to be transformed from a barren wasteland into a tropical forest planet . Through a special code , the computer was capable of being accessed , and directed to release steam , thus creating new climate changes such as bringing the rain season early .