Raids Unlock and Keys.

Yeti Cave [Level 25+]
Unlock: Get the quest from Wanderer Shore in square
Key: bring 2 "A stone imbued with magical properties" [drops from statue mobs in 3-9/10] to Yeti Cave quest NPC

Pumpkin Graveyard [Level 35+]
Unlock: Complete History 4-6
Key: drops from troll mobs in History 4-4/5

Cursed Ghost Village [Level 41+]
Unlock: get the quest from Legend 2-3
Key: bring 2 "Curious Snow Piece" [drops from snowmen in Legend Episode 2] to Legend 2-3 quest NPC

Kanhel's Ruins [Level 45+]
Unlock: Complete Legend 2-9
Key: drops from the Soul Ruler in Legend 2-9

Black Forest [Level 50+]
Unlock: get the quest from Luther Fred in square
Key: drops from mobs in Legend 1-1/2/3

Secret Cobolt Base [Level 50+]
Unlock: Complete either quest series in Legend Cobolt Field
Key: defeat the boss at Legend 3-4

Siren Sea [Level 50+]
Unlock: Complete Legend 4-8 up to the boss
Key: drops from mobs in Legend 4-6/7

Lower Jahillyah [Level 55+]
Unlock: Complete Legend 3-10
Key: bring 3 "Ancient Tombstone Piece of Al Hammura Temple" [drops from mobs in Legend 3-9/10] to Legend 3-9 quest NPC

Tumgalad [Level 56+]
Unlock: get the quest from Luther Fred in square, complete Shadow Valley and Sealed Forest
Key: bring 1 "Black Quartz" [from Shadow Valley] and 1 "Rune Crystal of Ancient Elves" to Sealed Forest quest NPC

Upper Jahillyah [Level 58+]
Unlock: Complete Legend 3-10
Key: bring 8 "Ancient Tombstone Piece of Al Hammura Temple" [drops from mobs in Legend 3-9/10] to Legend 3-9 quest NPC

Le Lua Secret Factory [Level 61+]
Unlock: Complete Legend 5-6
Key: defeat the boss at Legend 5-6

Research Lab Le Chattlie [Level 66+]
Unlock: Defeat Henry at Legend 5-10
Key: Defeat Henry at Legend 5-10

Cave of Chaos [Level 70+]
Unlock: Clear Forest of Moon for the first 10 floors
Key: Same Myth Key from Merchant

They're all easy exsept Research Lab Le Chattlie

That boss is so annoying. xD

Baphomet is the longest to get the keys.
I post this so everyone know where and how to unlock the stage and get the stage keys. Too many people asks the same question repeatedly.

Yeti's raid is 1 key per stone.

you can get yeti key box from yeti i believe(i got them sometimes while doing ep2 stages)

Put a big warning sign:
Yeti Cave SUCKS