The Onix Tunnel is a cave that possesses many stalagmites and stalactites. Despite the dangerous wildOnix that live inside, the cavernous pass is a shortcut through the mountains.
The Onix proved to be an obstacle for Team Rocket. Though for Ash and his friends, the shortcut was an easy walk thanks to Jigglypuff who sang the Onix to sleep. Brock deduced that the echoing properties of the cave probably made Jigglypuff's song stronger. Later, Team Rocket attempted to travel through again, but Jessie inadvertently disturbed the Onix. Subsequently, Team Rocket found themselves in some trouble, Jessie even wishing that Team Rocket was blasting off.