The Coruscant Underworld, also known as the lower levels, undercity, underground, underlevels, or Lower Coruscant, constituted the deepest and most deprived sections of the city-planet Coruscant. These areas were a blend of ancient, forgotten ruins dating back to the planet's earliest history, alongside contemporary, crime-infested establishments and nightclubs. During the time of the Clone Wars, a sizable ventilation shaft provided an entryway into the heart of this underworld realm.
The various districts and tiers ranged from the merely disreputable (such as the Uscru Entertainment District and 1313), with conditions steadily declining as one descended, to zones of perpetual darkness inhabited solely by overgrown vermin and zombie-like devolved humanoids. The streets of the underworld teemed with ruffians, and the walls and pathways served as habitats for a diverse array of bizarre creatures.
The majority of the underworld was situated more than a kilometer beneath the planet's urban surface and the platforms of the city. It was located underneath some of the most towering skyscrapers in the galaxy and other closely packed, spectacular structures of Coruscant, where only a scant amount of light managed to penetrate into the dim underworld.
Situated hundreds of stories below the peaks of the skyscrapers, the floors of Coruscant's urban canyons were perpetually shrouded in darkness. The presence of enormous buildings above caused the air to become trapped in the lower levels, creating a microclimate with at least three distinct layers. The trapped moisture led to rainstorms and convective wind patterns within these canyon floors. As a realm of artificial illumination, the lower levels of the galaxy's largest city offered the only affordable housing for many of its inhabitants. The constant rumble of machinery serving the elite above, streets haunted by exploiters and thugs, and walls infested with vermin, meant Coruscant's underworld hardened the resilient and consumed the vulnerable. With a population exceeding that of many star sectors, Coruscant's underlevels left millions beyond the reach of the planet's security forces. Local neighborhoods were at the mercy of hired criminals and extortionists. Vigilantes, demonstrating remarkable toughness, sometimes emerged to defend their communities from these criminals.
Waste materials were compressed into dense blocks and stored in the deepest recesses of the underworld. A great deal of the machinery that catered to the needs of the affluent surface dwellers was also housed within the depths of the underlevels, resulting in a constant sense of activity and unrest. Artificial light provided only a dim illumination to these dark and sorrowful levels. The underlevels were home to a variety of mutated species, including the cthon, Coruscani ogre, duracrete slugs, hive rats, shadow barnacles, conduit worm, taozin, and granite slugs, frequently posing a threat to sentient beings.
Information regarding the Coruscant underlevels during the Pre-Republic era remains scarce. By 100,000 BBY, the lowest fifty levels of the ecumenopolis had been fully constructed across the entire surface. It is believed that during this period, all native non-sentient species became extinct, with the exceptions of the Thrantcill (which evolved alongside the expanding city) and the Hawk-bat (which remained unchanged). Around this time, the highly intelligent Columi visited the planet and dismissed Coruscant as a primitive failure, despite the existence of the planetwide city.
In the millennia that followed, the lower levels became a haven for criminals and drifters. The bottom fifty levels constituting the underworld were buried beneath layers of duracrete and buildings. Several mutated species evolved during this era, including the humanoid Cthon and the corridor ghouls.
Despite the formation of the Galactic Republic in 25,053 BBY, life in the underlevels remained largely unaffected by the new galactic government. For millennia throughout the Old Republic era, the undercity remained relatively unchanged. During the Great Galactic War, food shortages sparked riots in the underlevels.
The higher sections of these decaying nether regions were home to seedy nightclubs, overlooked gambling dens, and trashy cantinas. The Uscru Entertainment District, featuring establishments like the Outlander Club and the Snapping Septoid, was one particularly dangerous yet popular location within the underlevels.
Black Sun, a once-renowned criminal organization, had numerous allies operating within the Coruscant underworld, including District Mayor Acros-Krik. Crime rates in the deepest levels of the underworld were so astronomically high that the government ordered many areas to be locked down. Enormous, impenetrable blast doors isolated these impoverished communities of desperate beggars and violent individuals from the rest of society.
Queen Padmé Amidala of Naboo and her security chief, Captain Quarsh Panaka, experienced the underworld firsthand when mercenaries took her hostage during her visit to Coruscant. Panaka gained access to one of the locked-down communities where the Queen was held by holding the door operator, an intellectual government agent, at gunpoint. After rescuing Queen Amidala and eliminating numerous criminals and hostiles, Panaka reopened the blast doors by uttering the passcode phrase "Coruscant has lovely sunsets."
Lower-class immigrants who arrived on Coruscant expecting to live in the prosperity of "surface life" gradually descended into the subterranean realms. Self-appointed neighborhood watchmen would often gain control over a small territory and their group of companions, potentially creating close-knit communities capable of withstanding hoodlum fights and minor attacks. However, once these vigilantes acquired weapons to defend their turf or engaged in violence, even in self-defense, their strengthening community was likely to succumb to criminal influences.
In 27 BBY, Ashaar Khorda and his accomplices attempted to exterminate the entire planet, including the underworld, using the Infant of Shaa. They hoped that destroying the galactic capital would lead to the downfall of the Galactic Republic. However, their attempts to use the infant were foiled by Zam Wesell, Jango Fett, and Yarael Poof, resulting in the deaths of Ashaar, his comrades, and Yarael.
During the Imperial era, which began in 19 BBY, conditions in the underworld worsened, transforming it into a haven for survivors of the Jedi Purge and dissidents. As a result of the Empire's strict control over all space traffic to Coruscant and the harshness of the ruling Imperials, many criminals sought refuge in the underworld. These individuals included bureaucrats who had made serious errors, diplomats from worlds punished by the Empire, and even clumsy servants and slaves from the Imperial Palace. Consequently, a clandestine culture emerged in the lower levels, as these fugitives were forced to remain there permanently. They survived by repurposing abandoned underbasement rooms, tapping into electrical conduits, stealing energy from the city's power grid, and subsisting on scraps and the fungus found in these lower levels.
Han Solo was once compelled to descend to the planet's very surface, an experience he found so appalling that he vowed never to repeat it, making the same vow for the surface of Nar Shaddaa. Sometime before the Battle of Endor, the Emperor ordered the construction and concealment of the Super Star Destroyer Lusankya beneath the lower levels of the planetwide city. The Lusankya became the private prison and secret headquarters of Ysanne Isard, the Director of Imperial Intelligence, who used it to imprison key Rebel Alliance prisoners.
Even after the New Republic liberated Coruscant from the Empire in 6 ABY, life in the lower levels continued much as it had for millennia. After Corran Horn, one of her captives, escaped, Ysanne Isard ordered the crew of the Lusankya to break the massive vessel free from the planet. As it departed Coruscant, the Lusankya devastated 100 square miles (259 km²) of the planet's surface, causing millions of immediate deaths and likely inflicting significant damage on a large portion of the lower levels. The Lusankya blasted its way through the two planetary shield levels, briefly exchanging fire with an orbiting Golan space defense platform, before jettisoning its lift cradle and leaving the Coruscant system.
In 10 ABY, the Imperial Inner Circle, emboldened by Grand Admiral Thrawn's devastating campaign against the New Republic, launched an attack on Coruscant and other key worlds. The combined Imperial armada bombarded Coruscant's energy shield from orbit, causing extensive damage to the heavily populated cityscape below, transforming much of the planet into a battlefield, and forcing Mon Mothma, the Chief of State, to order a complete evacuation of the capital's population.
Following the recapture of Coruscant, the Council decided to elect a new Galactic Emperor. Disagreements arose among the various admirals, generals, Moffs, Inquisitorius, COMPNOR, and Imperial Security Bureau officials, leading to an armed conflict between the Imperial factions on Coruscant. The city planet suffered extensive devastation during the conflict, with much of the planetwide metropolis destroyed by the fighting, resulting in billions of deaths.
After Palpatine's final demise in 11 ABY at the Battle of Onderon, the New Republic reoccupied the planet and deployed EVS Construction Droids to clear debris and construct new, gleaming skyscrapers. However, many of Coruscant's residents had fled due to the fighting, and the planet's population during the New Republic era may have been lower. Consequently, many of New Republic City's mid-level apartments remained unoccupied but serviceable. The shadowy lower levels, however, remained unaffected by the reconstruction program and continued to be the haunt of various crime syndicates, most notably the Lost Ones. Many still struggled to survive in the lowest forty or fifty levels.
In 23 ABY, the Second Imperium dispatched three Nightsisters named Tamith Kai, Garowyn, and [Vilas] to infiltrate the lower levels and recruit followers for their cause, including the street gang Lost Ones and Zekk. Those found to be Force-sensitive became Dark Jedi, while others became stormtroopers and TIE pilots.
The underworld endured throughout the years of Yuuzhan Vong domination, gaining new inhabitants. When the Yuuzhan Vong conquered and vongformed Coruscant into Yuuzhan'tar in 27 ABY, many Coruscanti sought refuge in the underworld to escape the Yuuzhan Vong. This event marked the formation of the Yuuzhan Vong empire, as they had claimed the galactic capital. Soon, however, the tunnels became the home of the Yuuzhan Vong outcasts—the Shamed Ones. Fleeing torment and persecution, many Shamed Ones fled to the underworld to find honor of their own. It was also here that Nom Anor assumed the identity of Yu'shaa and began shaping the Jeedai heresy into a genuine threat to the Elite.
The lower levels also became home to various life forms brought in by the Yuuzhan Vong from their home galaxy. In 29 ABY, Coruscant was liberated from Yuuzhan Vong occupation by the Galactic Alliance, but the Inner Rim world of Denon served as the temporary capital of the galaxy. During that time, the surface world was reconstructed by the Reconstruction Authority, but the lower levels remained largely untouched.
Between 30 ABY and 44 ABY, the Coruscant underlevels were ignored by the new galactic government due to the reconstruction efforts and the need to maintain order throughout the wider galaxy following the end of the Yuuzhan Vong War in 29 ABY. As late as 44 ABY, the underlevels remained overrun with exotic wildlife brought in by the Yuuzhan Vong and criminals who had survived the Fall of Coruscant. This was because the Galactic Alliance was preoccupied with the chaos that followed the end of the Second Galactic Civil War.
The underlevels persisted as late as 137 ABY, with one notable resident being the Hutt crimelady Queen Jool, who owned Rik's Cantina. This cantina appeared to be located on the lowest level of the lowest fifty levels of Coruscant. Following the failed Ossus Project and the Sith–Imperial War, the underlevels became home to a large population of Vongspawn—sentient beings infected by the Vongspawn virus.