Just a quick guide to show where some easily missed items and recipe books are. This will not contain the locations of Key Items.
All locations are shown, when possible, and marked on the in-game map with attached location descriptions.
If you haven’t, go buy a circlet from Dominique. This will open up several crafting recipes you don’t have access to until you buy it.
If you’re keen on hunting as many breakable walls, floors and ceilings as possible; grab yourself a Detectives Eye passive shard! They drop from Seekers (eyeballs) in the Forbidden Underground Waterway. Having the shards grade higher, makes the search area much bigger.
Unfarmable Cooking Materials
There’s a handful of cooking materials that you can’t farm easily.
Black Pepper is found only from blue chests in the Underground Sorcery Lab
Miso and Soy Sauce are only found in blue chests in the Oriental Alchemy Lab
Recipe Book: Fish Dishes
The recipe book for Fish Dishes is located in the Forbidden Underground Waterway, in a green chest that you need Invert or High Jump to gain access to.
Recipe Book: Supreme Dishes
The recipe book for Supreme Dishes is located in a breakable wall in the Forbidden Underground Waterway, conveniently near a teleport room.
Twin Dragon Towers
Once you have Invert or High Jump, you can come back here to obtain a volume of Hair Apparent and the Pasta Dishes recipe book. They’re in two chests, right next to each other.
The Valkyrie Sword is also located here. You need to have progressed the game far enough to have the Dimensional Shift shard.
Once you have Dimensional Shift, you can enter the room with the Shield Outsider and teleport down into an off-screen area, where the chest containing the sword is located.
In the section of Forbidden Underground Waterway that is located directly below the Gardens Of Silence, the Voice Changer is located at the end of the hallway, just before you go down, inside of a breakable wall.
Valkyrie Tiara (Den of Behemoths)
The Valkyrie Tiara is hidden in an almost unnoticeable, breakable wall in the hidden room under the platform you fight Valefar (the boss with a top hat and poker chips) on in the Den of Behemoths.