"What is this thing?"
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Sanctum is a sacred or holy place or an inviolably private place or retreat.  It is also the name of two different rooms (in Metroid Prime 2: Echoes and Metroid Prime 3: Corruption).
Samus Aran's victory over the Emperor Ing in one and both Dark Samus and Aurora Unit 313 in the other resulted in the destruction of Dark Aether and Phaaze, respectively.