During chapter 14 of Final Fantasy VII Remake, you have the option to complete a side mission where you need to locate three different Corneo secret stashes. Many of them are scattered throughout the game, and locating them can be a bit difficult.
You should make sure to have this one when you go around completing other side quests during this chapter because you pass through several of these locations while working on others. Before you can obtain these chests, though, you need to get the key to unlock them.
To obtain the key, you first need to visit Mirielle, who is at Nuts ‘n’ Bolts Hill, over by Lookout Point. After you receive the Corneo’s Vault Note that’s on the ground near her, you can speak with Kyre. She gives you a quest to do battle at the Wall Market Colosseum against the Beastmaster and their Hellhound. The Beastmaster has a few new tricks up their sleeve, but they’re easy to take out as the initial fight against them. The Hellhound is much more difficult. You want to use Ice-based spells to take out its flames, and Cure spells to attack its purple flames.
After you complete this quest and return to her, she gives you Corneo’s Vault Key.
First location – Sector 5 Slums
The first stash is pretty easy to find. You can locate it on the way towards Sector 5 Central, close to the church in the Steel Mountain region. Use the key to unlock it and obtain an array of items. It has the Ruby Tiara inside of it.
Second location – Sector 6 Slums
The second cache is over by the Collapsed Expressway. You want to go down the right path when coming up the pathway. It’s a little way off to the left once you follow the narrow pathway. It’s a bit of a trek, but plenty of exceptional items await you. The Diamond Tiara is inside of it.
Third location – Sewers
The final cache is a bit more tricky to locate. It’s in the Former Disposal Area in the Old Trunk Line in the sewer system. You can find this by making your way through the main quest, while you’re inside Don’s mansion. Before Leslie goes up the ladder out of the sewers, activate the switch next to it. Wait until you activate it, and then run back the way you came and go down the second path to the right.
You need to fight the Sahagin Prince before you can obtain the cache, and two of its friends. You want to use fire against it. If you can stagger it quickly using fire, you won’t have to worry about its counterattack move while battling it. After it’s defeated, you can obtain the third and final Emerald Tiara. Finish the rest of the quest with Leslie and wait until you can freely move around once more.
Once you have all three tiaras, go to Marle, who you can find at Evergreen Park. She will reward you with the Art of Swordplay Vol. III Manuscript for your troubles.