For the tenth labor Hercules was to steal the red herd of cattle from Geryon who lived on the island of Erythia. Hercules started this journey by sailing to the island in a goblet that was given to him by the sun.
Before he got to the island he came to a straight that divided Libya and Spain. In this place Hercules split a mountain and now the rocks formed there are called the pillars of Hercules.
It was easy for Hercules to actually take the cattle because when Geryon came to fight off Hercules, he just clubbed him in the head and went on his way until Hera stepped in.
Hera had not wanted Hercules to complete this task so she made the bulls run away and scatter after Hercules had gathered them all one bull was left which the King Eryx had in his possesion.
The king agreed to give the bull back to Hercules if he could beat him in wrestling. Which Hercules did three times and then killed him and took the bull anyway.
After that Hercules then brought the cattle to King Eurystheus and he took them and sacrificed them to Hera after Hercules left.