The Realm of the Mighty is the final dungeon of Dragon Quest IX. It is a dark, corrupted, twisted version of what was once the Realm of the Almighty; Zenus and Celestria's world that lied beyond the clouds and even the Observatory. The only way to reach this place is via the Starflight Express and only if it is fully powered with Benevolessence. The Palace of the Mighty is the fallen form of the Temple of the Almighty. It is located on the top of Realm of the Mighty itself.
The main character reaches the Realm of the Almighty after he or she has found all seven Fyggs that fell to the mortals' world and has freed the Goretress' celestrians. After ascending to the realm and Celstria explains the situation of more celestrians being imprisoned in the Gittingham Palace's Oubliette, he or she must defeat King Godwyn and free the unsuspected main antagonist of the story. Then, the spiteful foe will ascend to this place and use the power he gained through grudge and wrath to turn it into his evil realm, The Realm of the Mighty and Celestria will encommend the hero one last mission: To go to the Realm of the Mighty and stop the destruction that the villain is about to unleash.
After the game ends and The Realm of the Mighty is back to normal the Hero/Heroine can visit the Realm of the Mighty again with Celestria's help, this is an opportunity to challenge the final boss as many times as wished.