Book excerpt: For most souls, the Greek Underworld was a world of eternal shadows. The dead were ferried across a river in a boat guided by the grim Charon, who demanded payment from each soul. As they disembarked, a low growl rumbled through the silence, and a huge creature with three heads emerged from the dank mist along the riverbank. It was Cerberus, Hades’ watchdog who guarded the gates of his realm. The souls arriving had nothing to fear from the beast—but any souls trying to escape would be torn to shreds. Once a soul entered the Underworld, it was Cerberus’s job to make sure it never left. Cerberus is one of the best-known monsters in Greek mythology. His story takes readers on an intriguing tour of the Underworld and inside his unwitting part in the Twelve Labors of Hercules. Despite his fearsomeness, Cerberus is not seen as evil; instead he is respected as Hades’ loyal protector, making him perhaps the most appreciated monster of them all.