The Assault on Dis is a military and strategic operation: not a simple journey but the taking of an infernal prison city. The group infiltrates the defenses of Dis, fights the guardians, confronts Hecate, and either gains control of the city or negotiates its exit.
It is a turning point: the group moves from the defensive (escaping) to the offensive (taking infernal territory). The group achieves its objective, partially or completely.