The Mask of Tornarsuk is the main artefact that Lara finds in Tomb Raider II: Golden Mask. It is an Inuit artefact found by Lara in an immense hidden kingdom of gold, on a remote island in the Bering Sea. The mask is made out of pure gold. It is also the key to unlocking the Guardian of the Kingdom from its prison.
We do not know whether Lara took the mask once she defeated the Guardian. The mask is not in Lara's treasure vault, so we could assume she left it at the Bering Sea, but we could also assume she may be storing it in another vault or location other than Croft Manor, or that she has destroyed it for some reason.
The Mask of Tornarsuk can re-animate the spirits of dead beings. When Lara found the mask, the spirits of Inuit monks that had long died were revived, and their spirits assumed the shape of human bodies.