Abomination's graveyard
The "abomination's graveyard" was a site with a large quantity of bones of members of the Great Houses who had been mutated into bestial shapes by the Yssgaroth taint. The graveyard was discovered by Grandfather Paradox's original Godfather-lieutenants, and its bones were used in Faction Paradox armour.
The Faction claimed that the graveyard was a relic of an alternate timeline where the Yssgaroth had won their war with the Houses. This claim was disputed by the Houses, who denied that alternate timelines existed. Even experts within the Faction speculated there may be more to the story. At any rate, The Book of the War speculated that the Godfather-lieutenants must have passed through the caldera to access the graveyard. (PROSE: The Book of the War)