The Vault of Gaul
Vast was his wealth, great was its protector
Dwarfs get loot Gaul is greedy and wants none but Gaul to bask in it's glory. Seals treasure away. Only accessible by the blood of his blood. Story of scary monster of fire and skin like steel. Blah blah dragon.
The Uderkith were long rumored to hoard their wealth in vast treasuries buried deep underground along their Black Roads. After the sacking of Mortvaal a great hoard of wealth found its way into the hands of the Uderkith. A fortune amassed by the First Men believed to outvalue even the opulence of The City of Marble by more learned groups. My own studies would place the fortune and somewhere between a small country and purchasing your own demiplane from Gordon & Sons Co.
Most natives of the Solemn Expanse have heard some version of tale of the vault, some great trove of dwarves treasure.
Variations & Mutation
How the dwarves came into possession of their vast wealth is one of many heated topics. Proud dwarves will insist that the Uderkith carved their wealth from the Earth and formed it with dwarven hands. Proud humans insist it was the fortune of their addresses pilfered through conquest and violence until their people had been blessed dry.
Many would be adventures, archeologists, and scholars would have you read their interpretations of the what ifs and could be. You being the intelligent and well-schooled individual choose the work of a proper authority and not some half baked librarian.