Memoria
Memoria is the final dungeon, and it sits outside the world entirely: you fly into it aboard the Invincible rather than walking to it, so it has no position on the world map. The game’s own location table holds no coordinates for it. The Crystal World lies at the far end of it.
When You Visit
You visit Memoria at this point in the walkthrough:
42) Memoria
Walkthrough
Walkthrough
Flying into Memoria on the Invincible (airship) and battling each of the mini-bosses on the way to Trance Kuja.