The Citadel Challenge was an exercise that was held in the training facility of the military complex in Tipoca City on the planet Kamino.
The Citadel Challenge was a capture-the-flag type exercise. Cadets had to make it through guard towers and standard infantry droids, climb the hill, and pick up the pole which disabled all the droids and laser cannons. There were many forms of cover, such as walls and crates. The laser cannons were set to stun.
The Citadel Challenge was often used to train cadet squads, such as Domino Squad and Bravo Squad, to see if they were ready to be sent into battle or not. When Domino Squad attempted the challenge, they were disorganized and initially failed, however, after learning to work together, the clones managed to pass the test and graduated.
Until his death during the Battle of Kamino, the malformed maintenance clone 99 served as janitor for the room that housed the challenge.