There are many secrets to find in Bloodstained: Ritual of the Night, but first, you'll need to go on the hunt for some keys.
Once you've found the four hidden room keys in Bloodstained: Ritual of the Night, you'll get access to special rooms. There's usually a powerful Boss in each of these secret rooms, and you'll receive a unique ability after defeating them.
You can revisit these bosses and fight them again to power up your new abilities. Some of these keys will be available in the later stages of the game, so beware of spoilers.
If you're just getting started, then check out our Bloodstained: Ritual of the Night beginner's guide.
Bloodstained: Ritual of the Night - secret keys and rooms
Carpenter's key and room
To get the Carpenter's key, you'll first need to find the Invert ability Shard. To get it, you'll first need the Deep Sinker ability to access Inferno Cave. Fight the Boss to receive the Invert ability, then head to Dian Cecht Cathedral to get the key. You're going in the right direction if you're moving towards the Hall of Termination.
You need the Invert ability to pass the spike traps and access the chest which holds the key. Pick up the key then head to the Oriental Sorcery Lab.
Carry on past the fast travel room until you find the locked door and head inside to face the Master Carpenter Boss. Upon defeating him, you'll receive the Chisel Barrage ability that launches a series of chisels at foes.
Warhorse key and room
You can find the Warhorse key in the Glacial Tomb, near the fast travel point. You'll need to the G Axe Outsider in order to loot the key from the chest. Once you've found it, head to the Garden of Silence and go for a ride on the chariot.
When it stops, jump over the rock and fall down the hole to find it on the left.
Head inside to battle the Revenant Boss, and he'll drop the Ruinous Rood ability when you kill him. This will allow you to throw a spinning boomerang blade at enemies.
Millionaire's key and room
To find the Millionaire's key, head to the East of the Den of Behemoths, then go to the section at the top. You'll need to fight a Silver Wolfman and a Marbas to get past this area, then invert the map to continue to your right.
Jump down off the ledge and carry on to your left until you see a green chest. invert the map again to access it and get the Millionaire's Key.
Next, head to the Hall of Termination, down from the boss room hallway. You'll see a ledge sticking out with a glowing locked door, so head inside and be prepared for an interesting fight.
You're fighting the Millionaire's Bane, which is an evil slot machine. When you defeat him you'll receive the Jackpot ability, where you can summon a slot machine to aid you in a battle.
Celeste's key and room
In the Hall of Termination, Double Jump up all the platforms in the room to the right of the save room and smash your way through the ceiling. You’ll find a room filled with chests and items as well as Celeste’s key.
In the Livre Ex Machina area, you’ll not be able to enter Celeste’s room. Inside you’ll see a series of music boxes and a chair on each side of the table. Sit on the chair to the right and a phantom will appear.
So far, all we can figure out is that Celeste's room has lots of music boxes in it, a very nice cat portrait and a spectre.