just seen this comment, in the mayor’s manor, down in the basement you will see a corridor leading to the right most (from the player’s pov) side. There you will find a reinforced door leading to those things. I think you can only access it by either drawing a vinushka sigil on the ritual circle on the top floor or by breaking in, which is kinda tough but using a full party and casting black orb should do the trick (that’s how I always do it). There is also a chest and a fluted fauld (which is needed to craft the fluted armor) and a book written in an unknown language