Eurydice was walking down the river side and then got bitten in the foot by a poisonous snake, and then that is why she went to the underworld
Orpheus went down into the underworld where Eurydice went when she died to see if he could get her to come back to life.
While Orpheus was walking down the cave his music distracted all of the gost because the music was so good, and even Hades was pleased by it.
While Orpheus was walking down the dark cave with his music the king Hades said go back to the light as quick as you can while while the sprits are still distracted by your music and dont look back while the spirit of Eurydice is following you or else she will come back to me.
Orpheus was running back to the light and it was hard and long to get back to the top and he didn't believe that the ghost of Eurydice was following him back to the top so he had turned around and when he turned back all he herd was a faint farewell and the ghost disappeared.
As Orpheus was singing about his lost Eurydice contempt fell upon him and then that is were he died, but ten that is when he was able to reunite with Eurydice as a ghost.