SOLVED. Horror vampire military takes over ruined schloss with T-shaped crosses embedded in the walls. [s]

[Sheherazahde]

Horror and Vampires. A military group is stationed in a Schloss that has T-shaped crosses embedded in the walls. They find one cross made out of gold and pry it out of the wall releasing an ancient evil.

I think I read it in the '80s or '90s

[Sheherazahde]

Yes! Thank you. I kept wanting to call it The Schloss!
But The Keep is clearly the book I am looking for.
Thank you!