The Nine Hells was one of the planes of The Multiverse. It was said to contain the headquarters of the Ferrim Pecunia, which itself was said to contain one of the remaining pieces of The Orb.
The Tower of Grey, on their mission to save the world, visited Ioun, goddess of knowledge, seeking information on The Orb, which was showing them images of location throughout The Multiverse. One of those locations was the Ferrim Pecunia, within the Nine Hells.
Later, the party infiltrated Ferrim Pecunia, and were sent on a Corporate Retreat to a strange place containing its own Ferrim Pecunia branch. This is most likely the Nine Hells, seeing as how Toby Treacletart found a Jade Pyramid here.