Apollo Sanctum

The Apollo Sanctum is the final dungeon of Golden Sun: Dark Dawn. It is found at the end of the Endless Wall, which can only be fully traversed once the three orbs have been collected. The Sanctum itself can only be explored if the player has collected the Umbra Gear.

Story
Once Sveta's Umbra Gear and the elemental orbs have been collected, Matthew & Co. can scale up to the top of Apollo Sanctum to activate the Apollo Lens and nullify the effects of the Luna Tower, ending the Grave Eclipse. Without the Umbra Gear's barrier of darkness, the group of travellers would be overwhelmed by the immense light that shines down onto the sanctum, so the armor acts as a counteract to the environment of the sanctum's peak. The 3 orbs are needed to grant Matthew access to the Sol Blade, the strongest weapon in the game, and a 'key' to open the sun doors in Apollo Sanctum and other dungeons around Weyard.

Once the Apollo statue in the centre of the sanctum's peak has moved all the lenses towards the Apollo Lens, Matthew and Sveta can activate the Apollo Lens, which focuses enough light energy from the other lenses to shoot a beam that quickly stops the Grave Eclipse. However, once they reach the ladder that leads to the Lens, the Chaos Hound arrives to stop them in a rage. Strangely, once Sveta approaches it, the beast seems to calm down. Sveta, in a panic, uses the Smack Psynergy on it, and the Chaos Hound becomes upset. Suddenly, Chaos Hound is surrounded in darkness, and Blados & Chalis teleport next to it, explaining that the Eclipse had changed it, but they also went through their way to give it a few more 'improvements'. They then say that now they can't lose because the darkness of the Luna Tower's Grave Eclipse gave them a power enhancement, and challenges Matthew and Co. to a battle.

Blados and Chalis are knocked down, and Chalis say that they have to go into their alternate plan. Chaos Hound then becomes engulfed in darkness and begin to suck in the Tuaparang duo. Blados in horror realises that he's being pulled in, but Chalis proclaims that if winning against Matthew's "whelps" means being absorbed into the Chaos Hound then so be it. Matthew & Co. in a final battle face off against the Chaos Chimera, and after an intense fight emerges victorious. Sveta goes up to the Chaos Hound, and finally realises the horrific truth: that it was really a mutated form of her brother, Volechek. While everybody takes in what happened, Matthew tries to climb up to activate the Apollo Lens, but he's knocked back due to the heart of the light in Apollo Sanctum coming from that one place. Matthew tries a 2nd time, but he fails again and "Arcanus" telepathically tells Matthew to stop and that he can't do it. Matthew attempts to climb up a third time and fails.

Sveta, who has finished weeping for her near unconscious brother, walks up to Matthew but collapses on her knees. Kraden says that she absorbed too much light on her way to the Apollo Lens, and if she were to absorb any more she would surely die. But Matthew willfully decides to lend Sveta his spirit, and together they head up Apollo Lane. Once they reach the top, however, Volechek/Chaos Hound jumps to the top and knocks Sveta off the platform. Matthew's spirit falls straight back on him, and he jumps up and catches Sveta before she hits the ground. Chaos Hound, reverting back to Volechek for a split second, says sorry to Sveta for what he's put her through, and activates the Apollo Lens. The Lens shoots a laser of light towards the Luna Tower, which ends the Grave Eclipse and Volechek's life.