Phorose's underground tunnels.
Phorose was home to ancient temples and cities built long before the Clone Wars. During that conflict, the Galactic Republic battled with the Confederacy of Independent Systems, in an attempt to prevent the Confederacy from invading the world. Led by Jedi Master Plo Koon and Padawans Barriss Offee and Ahsoka Tano, the Republic forces fought back the Separatist Droid Army but left most of the capital city in ruin.
During the fighting, Jedi Offee attempted to rescue a community of native Ru, but was unable to prevent them from being killed in the fighting. Believing that the Republic and the Jedi Order were culpable for their deaths, it was this event that encouraged Offee's disenchantment with the Republic war effort and the Jedi's place in it.