Reach Sea 3
Go to the Haunted Castle
Find the Soul Guitar puzzle area
Collect the required items:
1 Dark Fragment
1 Hallow Essence
50 Ectoplasm
250 Bones
5 Vampire Fangs
5 Demonic Wraiths
5 Ghosts
5 Zombies
5 Reapers
5 Curses
Solve the Soul Guitar puzzle
Claim Soul Guitar from the puzzle reward