The Dungeon: Level 9 - Forge of the Fire Giants

The Pool of Fire has been commandeered by a larger than usual Fire Giant, named whatever you need him to be named, and his three young apprentices.  These black stone caverns have high vaulted ceilings that allow the giants and their phoenix pet plenty of room to stretch.  The floors are black cinders and ash lit by passing orange and blue curtains of flame.  The heat of this place does 1 hp damage per round to everyone unprotected by magic.  (A draught of water from the Pool of Water will negate this effect for one day.)
The Dungeon: Level 9 - Forge of the Fire Giants
The giant smith brought a pack of hellhounds with them from the pit of fire, and use them as sentries near the only entrances.  The giants have also built a retractable iron staircase that they can pull up behind them to keep out unwanted intruders.

The Pit of Fire itself is a low obsidian wall of black glass surrounding a roiling and boiling flaming pit filled with black burning pitch.  Things that crawl out of the pitch are generally crushed by the giants, who are easily irritated when the work of their forge is interrupted.  The walls of the Pit Room are covered by the various tools of a smith, and an enormous anvil rests on a stone slab in the center of the room.

The Fire Giants use their troll slaves to prepare food and generally keep the area tidy.  The trolls, protected by simple charmed rings dare not try to escape from the living hell that is Level 9.  They may beg adventurers for mercy, but won't keep their word - once out of this part of the dungeon they go back to their thieving, backbiting ways.