Final Fantasy Anniversary Edition/Labyrinth of Time

The Labyrinth of Time is the fifth secret dungeon, and a new addition to the game for the AE version.

Unlocking
The Labyrinth is only available once the Four Fiends (Lich, Marilith, Kraken, and Tiamat) are defeated. (See the main walkthrough for details.)

Once the Four are defeated, head back to Cornelia town and talk to the shadowy figure standing around the fountain. Once he runs off, follow him to the Chaos Shrine. You will see he use a secret door at the back of the Shrine; once he's gone go to the same spot and press to open the door.

Chronodia
Chronodia is the final boss in the Labyrinth of Time after having moved up multiple levels. It turns out that the hooded figure is Chronodia and he says he lures powerful warriors. He is one tough boss to beat. He has 42,000 hit points and every 3-4 moves he casts the spell Seal which disables one of your abilities: Attack, Magic, Defense or Items. So bring a load of potions and ethers. It is much easier to beat him if you have a white mage and a black mage. The black mage's spell Flare causes 500 damage and Haste and Temper help to improve your attacks. You have to coordinate using Spells to heal and Items to heal to beat this last boss. It can take an hour or so. After you beat him, he says that he thought he was unbeatable and you get 1 experience and the status of a Fake God. He also drops the Barbarian sword that has an Attack of 157 - even more than the Ultima weapon that you get after going through the 40 levels of Whisperwind Cove.