The last labour was the most dangerous of all. Eurystheus ordered Herakles to go and capture the beast called Kerberos who was the three-headed dog that guarded the Underworld.

Before entering the Underworld Herakles appealed to the gods for some help. Hermes, the gods' messenger, and the goddess Athena offered to be his guides. They made their way into the Underworld through a deep, rocky cave. As they travelled through the deep dark tunnels they encountered the spirits of the dead. At last they came before Hades, the god of the Underworld, and Herakles told him why they had come. Hades agreed to let the dog go but only on one condition; Herakles had to capture Kerberos without using any weapons and without harming him.