Crown of Winter Flame (2005)

`From the introduction:

At the end of the Age of Demons, just as the giants began their rise to power, one fire giant struck a bargain with a powerful fiend, before the couatls could manage to bind him to the depths. This giant prince offered to hide the demon until after the scourging was complete. Seeing his imminent captivity, the fiend readily agreed. Little did he know that he was trading one form of captivity for another, as the hiding space was within the giant princes crown. Once the fiend was bound into the crown, the giant prince reneged on his bargain and used the knowledge of the demon to amass terrific power and attain everlasting life. Hidden away in a secret fortress deep in a jungle valley, the giant prince dreamt far greater dreams of conquest and total dominance.
...
"Beyond the sealed door a set of stairs descends into the depths. On and on it goes, for almost half an hour before it leads ends at a large chamber filled with iron pillars. Nine of these pillars are arranged in the center of the room in a grid pattern. Strange arcane glyphs are etched into the uneven scorched iron. The floor between the pillars is also scorched.

"Across the room stands a large fortified iron double door with an elaborate vaultlike lock—or rather a series of four locks. At each corner of the room, attached to the floor, is a large crank. The air stinks heavily of ozone."