How to defeat Thantor?

[KateMilton]

There was a module for the Dark Eye RPG in the late 1980s or early 1990 called "Elfenblut" (=blood of the elves). It was about an elven vampire (Feylamia) in Thunata. The arkania online quest might be a portation of or a sequel to that story.

Could be. I have to find two elves who were kidnapped by some apemen from Thunata. Instead I have found one elf who is a feylamia.

I never played it but have faint memories of reading it. There was something about an organ in the finale, the vampire either playing it or being destroyed by it or both.
So my question is: Do you see an organ anywhere?

YES! Actually there is some piano-like thing in the dungeon. But it is out of tune, so I left it behind. Probably I have to find a way to fix it somehow. 
Thank you for pointing me in the right direction!