buried in the blood-drenched earth
These barren lands of ice
She was an evil woman with an evil old soul
Piercing eyes emotionless
a heart so black and cold
Forever young, Elizabeth Báthory in the castle of your death
You're still alive, Elizabeth
Her disposal of mankind
Her acts of cruelty and her lust for blood
Makes her one of us
To bathe in pure fresh blood
She'd peasant virgins killed
Forever young, Elizabeth Báthory in the castle of your death
You're still alive, Elizabeth
Forever young, Elizabeth Báthory in the castle of your death
You're still alive, Elizabeth

As @timshanks1 mentioned it is reference to Elizabeth Báthory who was a countess in Hungary who murdered young girls and women and then bathed in their blood believing it would make her look young (stay young in appearance).
Lots of lines in the songs relate to this:
"old Hungarian skies" "Forever young, Elizabeth Báthory in the castle of your death" "Her acts of cruelty and her lust for blood" "Our ancient countess was refused her desires will To bathe in pure fresh blood She'd peasant virgins killed"
Not sure how to take some of Ghost's lyrics. Are they literally agreeing with her actions? Simply recollecting an historical account? Being satirical?

This song's about Elizabeth Bathory. And Satan.
LOL'd at this one. :)
LOL'd at this one. :)

As to sokorny's question to me this is the narrator, Papa, being in love with the Countess Bathory. He's proselytizing about this evil old woman with the cold black eyes that murdered virgin peasants to bathe in their blood to keep herself young and beautiful and how, because of that, she's not only part of their dark congregation but they are either currently lovers or it's an unrequited love. Personally I think it's the latter.
For those who don't know Countess Bathory was eventually found out and locked up until her dying day in a tower in her castle. To me the song is Papa saying his love is up in that tower, still alive, and he will eventually rescue her from her captors and they will live evil-ly ever after