What's the lore behind Buried Cathedral?

Question

Before being a haunted place this was inhabited by a race who was able to read write and build huge structures, and chances are that race was once related to elves somehow, but what's truth is that almost nothing remain of such civilization nowadays but undeads and old structures buried somewhere on tibia so:
 

1. Where is lore-wisely located the Buried Cathedral Nowadays in tibia?
2. There's any confirmation that was indeed Elvenkind the founders of this building? If not, do we know or there's any information about such founders? What race were them?
3. What's the language used in the remaining writings of this place?
4. What happened to the inhabitants of this place and the place itself? why it's buried?

Answer 1

In the past, monks and scholars inhabited the cathedral, which functioned as a school or study center. Until they were invaded by unknown negative entities, ghosts, or spectres that made the cathedral what it is now: a haunted place. The cathedral was always hidden to serve as a refuge for its monks, scholastics and students. For gaining the entrance, there was a connecion of three passages that served as a nexus to the hidden cathedral that is now haunted (the cellar, the temple, and the tomb - which now are the 3 spectres hunting places).

A relationship with the elvenkind is that of the arachnophobicas and the thanatursus, which are creatures made not of dreams but of nightmares. 

Comments

That's an amazing answer, I wish it could explain a bit further where is the buried cathedral itself (map shows it's below roshamuul but the mobs seem equally to the corruption on elven courts).

About the rest, there are some discrepancy that simply are unresolved,  the ward stones that protected the dream courts,  the language used to unlock faceless bane, which race built it and what was their relation (before the corruption) with elves, it shows that we are missing important information about this place, but thank you anyway.