The Undercity existed in the depths of the city of Sundari, which was located on the planet of Mandalore. During the Galactic Republic's attack against Maul's forces, who were in control of Sundari, the one-time Sith apprentice made his home in the Undercity. Prime Minister Almec ordered Gar Saxon's Mandalorian super commandos to rendezvous with Maul in the Undercity when they encountered more resistance than they expected. In the Undercity, Republic troops under the command of ex-Jedi Ahsoka Tano and Clone Captain CT-0292, known as "Vaughn," were lured into an ambush that resulted in Vaughn's death and a face-to-face encounter between Tano and Maul.