Name: Coruscant underworld
Points of interest: Happyland, Rik's Cantina, Slum district G17, Uscru Entertainment District, Outlander Club, Snapping Septoid
Known non-sentient species: Duracrete slug, Stone mite, Conduit worm, ooka
Description: The Coruscant underworld, lower levels, undercity, underground, underlevels, or Lower Coruscant, were terms used to describe the lowest regions of the city-planet of Coruscant, laid with a mixture of ancient and forgotten ruins from the planet's prehistory along with modern-looking, crime-ridden venues and clubs. During the Clone Wars, a massive ventilation shaft offered access to the heart of the underworld.
Different regions and levels ranged from the merely seedy (such as the Uscru Entertainment District and 1313), progressively worsening as one descended, ending in areas of unending darkness populated solely by hypertrophied vermin and zombie-like devolved humanoids. The underworld's streets were riddled with thugs and the walls and streets were home to all manner of strange creatures.
Most of the underworld rested more than a kilometer below the urban surface and city platforms. It was beneath some of the greatest skyscrapers in the galaxy and other closely-spaced spectacular buildings of Coruscant where few rays of light filtered through to the gloomy section known as the Underworld.
Lying hundreds of stories below the skyscraper pinnacles, Coruscant's urban canyon floors never saw the light of day. Due to its enclosure by larger buildings, air was trapped in the lower levels, creating a micro-climate of which there were at least three layers. Trapped moisture contributed to rainstorms and convective wind patterns within the canyon floors. A realm of artificial illumination, the lower levels of the galaxy's largest city were the only affordable areas for many of the planet's citizens. Rumbling with machines that served the elite above, its streets haunted by exploiters and thugs, and its walls riddled with vermin, Coruscant's underworld toughened the strong and consumed the weak. Coruscant's underlevels harbored a larger population than do many entire star sectors, leaving millions beyond the protection of the world's security force. Local neighborhoods were at the mercy of hired thugs and extortionists. But the toughest faces sometimes belonged to vigilantes, who chose to defend the people on their own land from criminals.
Garbage was compressed into thick blocks and stored in the deeper levels of the Underworld. Much machinery that satisfied the needs to the well-to-do surface-dwellers, were also kept in the depths of the Underlevels and so there was a constant sense of motion and unrest. Artificial lighting barely brightened the dark and sorrowful levels. The Underlevels were home to various mutant species including the cthon, Coruscani ogre, duracrete slugs, hive rats, shadow barnacles, taozin, and granite slugs, which often posed a threat to sentient beings.
Very little is known of the Coruscant underlevels in the Pre-Republic era. In 100,000 BBY, the lowest fifty levels of the planetwide ecumenopolis had been fully built over the entire surface. During this period, all native non-sentient species presumably became extinct with the exception of the Thrantcill (which began to evolve with the new city) and the Hawk-bat (which stayed the same). Around that time, the big-brained Columi visited the world and dismissed Coruscant as a primitive failure despite the presence of the planetwide city.
Over the following millennia, the lower levels became the domain of criminals and vagrants. The bottom fifty levels that made up the underworld were buried under levels of duracrete and buildings. Several mutant species developed around this period including the humanoid Cthon and the corridor ghouls.
Despite the formation of the Galactic Republic in 25,053 BBY, life in the underlevels was left unchanged by the new galactic government. Millennia after millennia during the Old Republic era, the undercity stayed the same. During the Great Galactic War, food shortages caused riots in the underlevels.
During the waning days of the Galactic Republic period, while the wealth and marvel of Coruscant gleamed on its exterior level, the Underworld below degenerated even further, since the Republic was in decline. It served as a refuge for scum, petty crooks, as well as drug dealers, the poor gone bad, and other outlaws. Even the highest of the underlevels fell into ruin and disrepair by the time of the Naboo crisis and the Clone Wars. Seedy nightclubs, overlooked gambling corners, and trashy cantinas were actually areas of some of the higher sections of these run-down nether levels. One place as dangerous as it was popular in the Underlevels was the Uscru Entertainment District with such hangouts as the Outlander Club and the Snapping Septoid.
The once-famous criminal organization called Black Sun had many allies working in the Coruscant underworld including none other than District Mayor Acros-Krik. The lowest levels of the Underworld had such an unbelievable crime rate that many areas were locked down by order of the government. These poor communities of desperate beggars and violent people were isolated from the rest of society by enormous, impenetrable blast doors.
Queen Padmé Amidala of Naboo and her head of security, Captain Quarsh Panaka, got to see the Underworld firsthand when she was taken hostage by mercenaries during her visit to Coruscant. Panaka was given access to one of the locked-down communities where the Queen had been taken by holding the door-operator, an intellectual government agent, at gunpoint. Once rescuing Queen Amidala and killing much scum and hostiles alike, Panaka re-opened the verbally-accessible blast doors by giving the passcode phrase "Coruscant has lovely sunsets".
Lower-class immigrants who came to Coruscant, expecting to be living in the prosperity of the "surface life", were all gradually sunken into the subterranean realms. Self-made neighborhood lookouts would often gain some small territory over their group of companions and lessers (if lower ranks could at all be possible), thus occasionally creating a tight-knit and durable community who might have even withstood hoodlum fights and minor attacks. Usually though, once these vigilantes acquired weapons to protect their turf or began engaging in violence, even if in self-defense, there was always a great chance their strengthening community would collapse to eventual criminal influences.
In 27 BBY, Ashaar Khorda along with his associates attempted to euthanize the Coruscant Underworld, along with the entire planet itself with the Infant of Shaa. The destruction of the galactic capital was hoped to be followed by the destruction of the Galactic Republic. However, their attempts to use the infant were thwarted by Zam Wesell, Jango Fett and Yarael Poof. This resulted in the deaths of Ashaar, all his comrades, and Yarael.
During the Imperial reign of the galaxy that began in 19 BBY, conditions in the Underworld deteriorated further and it became a refuge for Jedi Purge survivors and dissidents. As a result of all space traffic to Coruscant being tightly controlled by the Empire and the harsh cruelty of the ruling Imperials, many criminals fled to the underworld. They ranged from bureaucrats who had made serious mistakes in their work, to diplomats from worlds punished by the Empire, to even clumsy personal servants and slaves from the Imperial Palace. Thus, an entirely shadowy culture developed in the lower levels since the fugitives were forced to remain there for all their lives. These fugitives survived by revamping some of the abandoned underbasement rooms, tapping into electrical conduits, and stealing energy from the city world's power grid, while surviving upon scraps and the fungus found in these lower levels.
Han Solo was once forced to descend to the very planetary surface itself, an experience he found so harrowing he vowed never to do it again, making the same vow for the surface of Nar Shaddaa. Also, at some time prior to the Battle of Endor, the Emperor had the Super Star Destroyer Lusankya constructed and hidden beneath the lower levels of the planetwide city. The Lusankya would become the private prison and secret headquarters of the Director of Imperial Intelligence Ysanne Isard, who would use it to imprison key Rebel Alliance prisoners.