The Fractal Treasure Fortress of Yre is the priest court of Mammon, and the headquarters of the Bank of the Grand Dragon.
Mammon rarely leaves it.
Mammon had Zaid imprisoned in the treasure fortress of Yre by very tenuous agreement after the last Concordance of the Demiurges.
It contains the fractal vault, an impenetrable treasure hoard that the devil syndicate under Himself wants to get into. This may be useful to certain heroines.