In the Twelve Labors of Hercules, what did Hercules clean in a single day?

Hercules cleaned the Augean stables in a single day during the Twelve Labors.

The stables belonged to Augeas, king of Elis, whose enormous herds had produced years of accumulated manure. The task seemed impossible because the buildings had not been cleaned for a very long time. Hercules approached the problem as an engineering challenge instead of using only physical labor.

He diverted the rivers Alpheus and Peneus through the stable complex. Their rushing water swept away the accumulated waste and completed the cleaning rapidly. In some versions, Hercules demanded payment from Augeas or made an agreement before starting, which later caused a dispute.

Eurystheus did not count the labor because Hercules had sought payment and because the rivers, rather than Hercules’ unaided labor, did much of the work. This explains why the stable-cleaning episode is remembered as both a legendary feat and an example of the phrase “Augean task.”