Helheim
From WikiRaider
Helheim, the Norse Underworld, is actually Xibalba and Avalon. Natla tells this to Lara in the Mediterranean level of []Tomb Raider Underworld]], and that no one can enter without Thor's Hammer.
Helheim is where Lara's mother actually is. In one of the gameplay trailers, Lara tells Zip what she heard from Natla; "Helheim, Zip. Various myths use different names, but they all apply to the same remnants of the ancient world".
The final level of Tomb Raider Underworld takes place there.
