Floor 23
From The Unofficial POWDER Wiki
H'ruth: Prove your worth in my combat arena!
H'ruth's arena is a linear series of rooms (only one entrance and one exit per room), each with one or more monsters of increasing difficulty. There are numerous traps as well. Like in Quizar's maze, the enemies don't respawn, and you can neither teleport nor dig through walls.
As long as you've got decent stats by this point you should be fine, since you can pretty much rest after every room until you're at full health/mana. (The monsters can't open any of these doors, unless you've opened them first). Possess can also be used to fearsome effect on this level, especially with Warning. For a full rundown and list of the challenges, see the rooms page.