Serenno City was a city situated in a valley. This location was near Castle Serenno, which served as the headquarters for House Serenno. During the time that Dooku, the former Jedi who became a Sith Lord, reigned as Count of Serenno, the city existed below the cliff where the castle stood. It was also opposite the eastern ridge on the Outer Rim planet known as Serenno. The city's position placed it in proximity to the upper forest region of the planet, beyond a nearby forest. Following the conclusion of the Clone Wars, the Galactic Empire destroyed the city using an orbital bombardment. In 19 BBY, Hunter and Wrecker, members of Clone Force 99, attempted to use the ruined city as cover to evade Wilco's company commanded by Clone Captain Wilco.
When the Clone Wars began, pitting the Galactic Republic against the Confederacy of Independent Systems, Dooku financed his war efforts by exploiting not only other planets but also by stealing from his own citizens, including those living in the city. After Dooku's death, which occurred shortly before the Clone Wars ended, the Galactic Empire, which rose from the ashes of the Republic, conquered and occupied Serenno. The city faced destruction via orbital bombardment, which forced surviving Serennians, such as Romar Adell, to seek refuge in hiding places, such as Serenno's upper forest region.
Sometime after the city was reduced to rubble, members of the rogue clone commando unit known as Clone Force 99 made an attempt to steal a portion of Dooku's war chest while Imperial forces were in the process of preparing it for off-world shipment. As events took a turn for the worse, the squad became separated, and the team's leader, Hunter, along with his comrade Wrecker, made their escape into the city's ruins in an effort to evade Clone Captain Wilco and his company of clone troopers.
Wilco spearheaded a pursuit into the city, establishing visual contact with the two renegade clones as he attempted to encircle them. Wrecker, displaying his resourcefulness, fashioned a makeshift cannon from the remains of a destroyed Separatist tank, employing it to blast a path through the Imperial forces. Hunter and Wrecker successfully fled the city's ruins, returning to their starship, the Marauder, to gather the remaining members of their team before departing from the planet.
The city's initial appearance was in the Star Wars: The Clone Wars third-season episode "Nightsisters," although its exploration as a location occurred in the Star Wars: The Bad Batch second-season episodes "Spoils of War" and "Ruins of War." Molly Denmark was responsible for the exterior city lighting concept, and she also created the lighting concept for an Alpha-3 Nimbus-class V-wing starfighter flying above the city.