Unlockable          How to unlock
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Earthgift Shrine  - Defeat Lich in the Cavern of Earth.
Hellfire Chasm    - Defeat Marilith in the Mount Gulg.
Labyrinth of Time - Defeat Lich, Marilith, Kraken, and Tiamat. 
                    Visit Chaos Shrine to unlock.
Lifespring Grotto - Defeat Kraken in the Sunken Shrine.
Whisperwind Cove  - Defeat Tiamat in the Flying Fortress.