Beginning: It's the completion of two main quests linked with each other, begun in [44-M] Subconsciousness / Consciousness (1/2).
After completing three tasks connected with subconscioussness and finding the solutions to Nanook's conflicts, stand in the middle of the hall with three doors. You'll fall deep into it and you'll emerge in . Nearby there's an altar of endurance you can use before the fight that awaits you. Run to  and watch the cutscene. You'll square up to the last boss in the game - Subconsciousness.
It's a strong and tough enemy who strikes with deadly blows, and on top of all that he can also throw fireballs. Start attacking him, but once he sustains serious injuries his health will return to a maximum. The protection shields of the four altars in , ,  and  will be taken off for a short while, and the boss will stop attacking. You must definitely use it to your advantage - run to one of the crystals, kill a spider-like Terror and destroy the Altar.
You can first kill all Terrors if you like. This way, nobody will attack while you'll be destroying the altar, however, it's best to concentrate on the latter activity. It's highly unlikely for you to destroy the second before the protection shields appear again, and then you'll have to painfully wound Subconsciousness once more.
Repeat the actions described here until all Altars are destroyed. Killing the Subconsciousness won't be a problem then - do it (you'll get 15,000 XP), take Map of Nanook's Consciousness, and then teleport to the ship using the portal in , which Reality Weaver will create.
You'll appear in . Run to the stairs and get to the very top level of the ship, and then go to Nanook's cabin. Talk to Geoffrey, and then to Nanook. It doesn't matter whether you say you look for the treasure or you want to free all the souls. However, the next choice among the three dialogue options means three different game endings. All have been described below. Finish the conversation with Nanook after making a choice.
1: "Happiness. Help me find it."
If you've decided to choose this option, you'll receive The Map to Happiness. Finish the conversation with Nanook and then look through the quest  The Treasure (2/2). When you've completed it the game will end.
2: "There's nothing."
Nanook will be very surprised that you don't want anything. Finish the conversation with Nanook after choosing this option, and watch the cutscene showing your character going away in search of new adventures. The game will end then.
3: "The spirits, Lora and James: I wish to know the..."
Nanook will be very surprised that you do want something but not for yourself. Finish the conversation with Nanook after choosing this option, and watch the cutscene showing your character giving Lora and James a map that will help them find their bodies. The game will end then.