Here is another installment of exTRAPaganza, our Thursday over-the-top trap series.
The floors are covered in a very fine sand. Unless caution is taken, each action taken in the sand stirs up dust.
At the start of each turn, the pc must make a DC 0 Constitution saving throw, or breathe in dust. If the saving throw fails, the target takes 1 Con damage and becomes fatigued. Once fatigued, this has no more effect.
A creature can attempt to make an average difficulty Dexterity (Acrobatics) check before each move or attack action to not stir up dust. If it fails, it stirs up dust. Every time the dust is stirred up, it increases the DC of the Constitution saving throw by 1. This is a cumulative effect. Each minute that passes where no dust is stirred up decreases the DC by 1.