The Ruins of Castle Thanath

It has stood here for as long as anyone can remember. No records exist that speak of a time when it wasn't a crumbling shell of a castle. As if it was built as a ruin in the first place. Then comes the obvious questions: who built it, and why?  

— Notes scribbled down in an old diary covered in spiderwebs,
found on a table on the first floor.

General

The Ruin of Castle Thanath could as well be as old as time itself with how long it has stood on the cliffside.
All reconds available from every possible source has always noted that it is an ancient castle ruin with no known builder or owner, dead or alive.
Its architectural design appears timeless and all-encompassing: if one looks closely enough it has something from every culture from every corner of the world that flows into each other seamlessly.  

— Excerpt from A scholarly study of Castle Ruin Thanath.

Who was Thanath?

This is a question nobody really can answer but it has always been the name on the ruins for as far back as any crumbling records show.
To try and find who this Thanath was have been futile: it can be the name of the owner as well as the builder. Maybe it was named after the cliffs it resides on, rather than the opposite. We might never know.  

— Excerpt from A scholarly study of Castle Ruin Thanath.

The ruins in short

The ruins consists of two buildings that are three floors high and connected via an decrepit stone bridge. A tall tower is connected to the southeast building that reaches up about five floors.
All windows are just empty openings in the stonework, from which the howling of the winds can be heard from at a distance. To some, it sounds like the wailing of a lady, while to others the howling winds remind one of the cries of children, or something more otherworldly.  

— Excerpt from A scholarly study of Castle Ruin Thanath.

Entering the hallway

The largest of the two buildings is the one connected to the tower. The large gate is made from oak or a similar wood and covered in cast iron covered in minuscule etch marks. It opens with a tiny creaking sound and into a fairly long hallway.
Along the sides stands statues of various designs that look like they change places with each other if you look away from them for a moment. Their appearances vary depending on who enters, that, at least is the general assumption as no one appears to see the same designs.  

— Excerpt from A scholarly study of Castle Ruin Thanath.