From WiKirby, your independent source of Kirby knowledge.
Cannon Tower is an enemy that debuted in Kirby: Triple Deluxe, first encountered in the Fine Fields level. It can only be defeated with the Hypernova ability.
Cannon Tower consists of a rotating brickwork cannon, which fires a missile, then turns around before attempting to fire again. It has a weak point on its backside which, if hit, will cause it to shatter. Kirby needs to inhale the missile it shoots, then hit it on its weak point with the same missile.
Cannon Tower may also come in stacks, which usually keep a doorway locked up top. In such instances, the last Cannon Tower will usually have a surprise attack, which consists of shooting out a long spiky bar, then spinning around with it.