From the center spawnpoint in Glastheim (P), head north into the church (Located at 200, 133)
Inside, head straight forward, then take a right by the piano to head into the side room (Located at 219, 279)
From there, head forward and speak to the Spirit (Located at 275, 284) to start this quest.
The spirit will ask you to help exorcise his friends, which have been trapped in the future. After accepting his quest, head to Glastheim, the normal map with mobs on it. Located randomly on the map are various ghostly looking mobs similar to those you'd find in Bio Labs. Kill approximately 20 of these mobs, and you should get a message that says to head back to the Spirit.
Return to the Spirit, and he'll thank you by rewarding you with a Ghostie