"He who is valiant and pure of spirit may find the Holy Grail in the Castle of Aaargh"
Depending upon the most recent inhabitants of the dungeon:
Actual Dungeon Prisoners - Date ticks, tick tack toe, ticks for lunar phases, long division, epic ballads, detailed treasure maps, bad poetry, amazing poetry, insane ramblings, prayers, curses, exploding runes...>BOOM<
Small Evil Critters - Violent cartoons, excrement, more violent cartoons, hexes, wards against invaders, still more violent cartoons, chalk outlines, dead things pegged to walls and floors
Big Evil Critters - Big claw slashes...and my creativity just ran dry...to be continued