I've got a great mix on my MP3 for the line that will be waiting outside to get into the haunted house but I can't seem to locate just some eerie - plinky - not necessarily a real song - piano music for the inside of the haunted chamber...
Anyone have any ideas?

What about the theme from Candyman? If you scroll down the page you can listen to it.

MIDI Movie Theme Songs & Video Clips - C

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"Sounds like a lot of supernatural baloney to me."
"Supernatural, perhaps. Baloney, perhaps not."

Not sure how eerie you need - but the Death March by Mozart is my favorite for Halloween.

One of the BBC Horror Sound Effects LPs had 3 or 4 eerie piano tracks on it.

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