Ironslag

In the icy mountains north of the lake on the Giant Island sits Ironslag, the fortress home of fire giant Duke Zalto.
Irsonslag is not only a fortress but also a massive forge, where iron ore mined from within the mountain was once smelted and turned into axes, war hammers, and other mighty weapons. Abandoned thousands of years ago, it has been restored and reopened by Zalto, who seeks to rebuild a colossal war machine, the Vonindod, that will allow him to wage an epic war and rise through the ranks of the giant lords.
Anyone who dares venture into Ironslag will face treacherous Firbolg, formidable salamanders, powerful fire giants, and the terrible duke himself - plus his equally dangerous family.

Geography

The caverns that form the forges and halls or Ironslag are concealed behind a five-hundred-foot-tall cliff face. Visitors must navigate their way past a village of treacherous Firbolg and through a labyrinth of mines before finally reaching the foundry and the personal quarters of Duke Zalto and his family.

Description

The sprawling complex of Ironslag is most quickly entered through fifty-foot-tall adamantine doors that can only be opened by a fire giant's magical command. Since they're unlikely to open the doors to adventuring parties, you'll have to take the long way around, through the Firebolg village and into the mines.
Firbolg Village: A small and seemingly idyllic settlement, but its fields and mill are operated by slaves. The Firebolg are very welcoming, because every stranger is another potential captive.
The Mines: This confusing maze of tunnels is linked together by rail tracks for iron carts, Salamanders, fearsome half-humanoid, half-serpentine fire elementals that thrive in molten heat, keep an eye on the dwarfs and gnomes forced to work here.
The Foundry: Ogres on the upper section of the foundry tip iron ore from the carts into the smelters, while fire giants below keep the smelters burning so the ore can be melted down to make weapons. The foundry is unbearably hot.
Assembly Hall: The main hall of the fortress, where the parts of the Voninhod hang suspended by chains from a ninety-foot-tall ceiling, and where Duke Zalto himself often sits at his throne, attended by his fearsome giant hounds, Narthor and Zerebor.
The Forge: A forge so hot it can melt and mold any metal into weapons and armor. The energy required to power it is very rare, so it has lain dormant for thousands of years.

The foundry

The foundry at Ironslag is where iron ore mined from the mountain is melted down to be turned into weapons. The overseer of the foundry is Duke Zalto's spoiled and lazy teenage son, Zaltember. When adventurers encounter Zaltember, the young fire giant may be threatening to toss a prisoner into the molten iron below, simply for his own amusement.

The Vonindod

The Vonindod, (meaning "titan of death" in Giant) is a colossal construct used against dragons during the Draco-Giant War.
The Vonindod stand 80 feet (24 meters) tall, three times taller than any titan, and is humanoid-shaped with a horned helm and a greatsword. It is almost entirely composed of adamantine with huge rubies for eyes.