Ice Castle

Ice Castle is a Second Sea island for players between Level 1350 and 1425. It is a vast island with a massive castle towering over it and flat chunks of ice floating on the water in front. The Frost Quest Giver offers three quests: defeat 8 Arctic Warriors at Lv. 1350 for 12,250 Beli / 41,000,000 XP, defeat 8 Snow Lurkers at Lv. 1375 for 12,500 Beli / 43,000,000 XP, and defeat the Awakened Ice Admiral at Lv. 1400 for 20,000 Beli / 45,000,000 XP. Other NPCs include the Boat Dealer, the Luxury Boat Dealer, a Set Home Point and, sometimes, the Barista Cousin. The Awakened Ice Admiral drops the Library Key, and the Hidden Key drops from the Arctic Warriors, Snow Lurkers and the boss. Using the Library Key on the castle door opens the way to Phoeyu, the Reformed, who teaches Death Step, and the wiki says that door stays unlocked after you leave. The Hidden Key opens a black chest with a keyhole under the side of the stairs where the boss spawns and rewards the Legendary sword Rengoku, but neither key is saved if you leave the game. The island has 9 chests: 1 Diamond, 5 Golden and 3 Silver. High-level players often visit for the Hidden Key, so stay alert while grinding.