Collapsed Passageway is a discovery sidequests in Chapter 6, "Light the Way", in Final Fantasy VII Remake, taking place in the Sector 4 Plate. While traveling to reach Section H, Cloud Strife attempts to cross a passageway to reach a 
Support Materia. However, as he does so, the passageway collapses, blocking his path forward.
This discovery sidequest can only be completed once. If a player completes it and later returns via chapter selection, the quest does not trigger.
Walkthrough[]
The sidequest begins once the passageway falls. It cannot be accessed immediately until "Power for the Platform" when the party has reached Section H. After deactivating the second sun lamp, on the path to the third sun lamp, a ladder leads down to a lower level, just to the right of the first platform after moving across to it. Here, two queen grashtrikes are fought. Stay defensive during the fight, and use 
Blizzard (or Blizzara) against them, along with character abilities to stagger them, then use Tifa's martial techniques with Unbridled Strength to increase their stagger damage taken, and lay into them.
After defeating them, a console on the platform can be accessed to move a bridge. First, move it all the way down to access the 
MP Up Materia, then move it partially back up so a bridge across is created. Cross the bridge and run to the end of the platform for the Elemental Materia. This is a powerful materia that can be linked to a 
Magic Materia on weapons to imbue physical attacks with an element that exploits an enemy's weakness to deal increased damage, or on armor to resist elemental damage. When used on weapons, this is most useful on Tifa, who has the best Attack Power attribute and thus relies on physical damage, though it is also useful on Cloud who is likely to have magic materia equipped anyway, meaning a slot will be useful in general. When used on armor, it is useful on any character.
In a repeat playthrough when the elemental materia has already been picked up, there is a Healing Materia in its place.