Continuity mistake: After the frisbee is taken away from Hercule's, he sadly sits down on the edge of the fountain. Between shots the rocks and things on the ground distinctively change.
Continuity mistake: While watching today, I realized right before "Go The Distance' when Hercules' mother is putting the wrap on him, originally it's green, but throughout the song, it's blue. Part of me thinks that it's supposed to be the shadows from the sunset, but looking again, it seems that it suddenly changes from green to blue. Especially since during the lightning storm in the song the color doesn't change much at all.
Continuity mistake: When Hercules is running into the market with the wheelbarrow, as his dad cries, "Hercules, slow down," the donkey's leg is unbandaged and perfectly all right. This changes after Hercules arrives in the market.
Continuity mistake: Panic pulls open the tab on a soda can, but the can opens on the wrong side from the tab.
Continuity mistake: When the pillars are about to crash on the pot-maker, he has eight pots and his hand. Then after they don't, and he breathes in relief, there are only six pots in his hands.
Continuity mistake: When Hercules is proving to Phil how strong he is, he runs up a dirt hill and throws a part of a statue into the water. After he does this, the hill is now covered in grass.
Continuity mistake: When Hercules collapses after his battle with the hydra, the position of his arms changes between shots.
Continuity mistake: When baby Hercules is found, he's wearing a medal around his neck with a ribbon. The ribbon is tight around his neck, yet when the old man lifts the medal, the ribbon grows a couple of feet as he pulls it away from Herc's neck & turns the medal around to read it.
Continuity mistake: When the girls are mobbing Hercules, one of them steals his headband and then runs off with it. Seconds later, his headband is back in the room.
Continuity mistake: Before Zeus picks Hercules up, Herc's medal is untucked. Then when Zeus has him in his hand the medal is tucked in. When Zeus puts him back on the ground, the medal is gone, but Hercules has it again later in the movie.
Continuity mistake: When Hercules arrives in the market with his wheelbarrow, the angle of the brown line on one of the wheels changes between shots.
Continuity mistake: When Hercules says, "I want to become a hero, a true hero," Phil's door is closed. In the next shot, when Phil replies, "Sorry kid, can't help you," his door is open.
Continuity mistake: When baby Hercules is drinking from the bottle, Panic is holding Hercules' arm high in the air. In the very next shot, he is holding Hercules' arm down low, near his chest.
Continuity mistake: In the song "Zero to Hero", when Hades pushes the figurine of the boar towards the figurine of Hercules, Hercules' position changes between shots.
Continuity mistake: When Hercules' sword gets stuck in the stone during his battle with the hydra, the angle of the sword varies between shots.
Continuity mistake: When the girls are mobbing Hercules, Phil's flute magically appears around his neck.
Continuity mistake: After Hercules slices off the hydra's head a lot of green goop comes out of its neck and forms a large puddle. A few seconds later, as the hydra suddenly sprouts three more heads, the puddle of goop is much smaller.
Continuity mistake: After the cyclops has beaten Hercules up, Phil arrives to talk some sense into him and drops his handkerchief on the ground. Then when the cyclops picks Hercules up, the handkerchief is gone.
Continuity mistake: Hercules meets Phil. Phil walks away & enters his tree. Hercules grabs the door & yanks it off it's hinges. You can see there's a hinge on the door & another was left in the doorway's frame. Phil is hanging onto the door handle as Herc holds it up. After Phil lets go of the door, the door has both hinges.
Continuity mistake: When the pillar almost falls on Hercules, Meg dives head first to push him away. Then in the next shot, as Meg is crushed under the pillar, she's lying feet first.
Answer: I always assumed one of the gods told him how to get there after they won the battle. The underworld in Greek mythology could be traveled to by mortals, albeit extremely ill-advised.