This page of the FF7 Remake guide has information about another Discovery - Collapsed Passageway.
You will encounter an object hidden behind a broken bridge. However, to reach it you must first turn off all three lamps. Once you use the third lever and restore power to the Cargo Platform, you will be able to get the item. There is a ladder near the third lamp - it is right under the H-05 sign.
This battle is a challenge. You fight Queen Grashtrike and Royal Webbing. Enemies are very tough and they can also poison you - be vigilant. Try to focus on a single target and make it staggered, then use the most powerful attacks, such as Fira.
Now set the bridge in the right place to create a path. You can now go for the Materia.
Reward: Orb of Elemental Materia