The Coruscant underworld, also called the lower levels or undercity, were the levels underneath the surface structures of the planet Coruscant.
Skyscrapers towered above the highest level on Coruscant, Level 5127, upon which laid the Galactic City, but under the surface structures the levels of Coruscant descended down all the way to Level 1, which was deemed uninhabitable. The various levels of Coruscant were accessible by huge portals that also served as ventilation shafts. Covered by the surface structures, sunlight did not reach the lower levels leaving them in a perpetual state of darkness illuminated only by artificial lights for thousands of years. Undercity dwellers often had to breathe toxic fumes from millennia of urbanization, while wealthy citizens in the upper levels had access to rich and filtered air. Influential crime families operated in the lower levels of Coruscant, which were patrolled by the underworld police division of the Coruscant Security Force