The party comes upon a yawning chasm. On either side are rows of very wide and tall pillars reaching up to the shadows of the cavern roof. One of the pillars appears to have fallen over from one side of the cataract to the other, and can now act as a bridge. The pillar is wide enough that crossing it down the center seems to be safe and easy, if the characters take their time.
A successful detection of traps will, indeed, find one. When a character reaches half-way point, the pillar begins to spin like a roller. Anyone standing on it must make a successful Dex roll, or fall to their doom. After a minute or so, the pillar stops spinning, and resets.
Optional: It takes 1d4 Dex rolls to get across safely after the spinning starts.