Agon Temple

Description
Located deep into the Sllithàna Swamplands in the center of Agon Lake, far south from the civilized lands of Thale, Agon Temple is a pyramid like many other temples in the Swamplands. However, there are some key differences between it and the Swampland's other ancient places of worship to dark gods.

Firstly, it does not seem to be dedicated to any deity, exhibiting no known iconography or even markings of any kind. In fact, no one knows who made it or for what purpose. Not even the Celestials and Fiends have any memory of when or how. According to them, it appeared one day many millenia ago, showing signs of always having been there even before they themselves came into being, though they know that cannot be.

Secondly, it is far larger than any temple in the region, being over 450 ft high and 750 ft wide at the base. And those measurements are simply at surface level. Since there are no known records of Agon Lake's depth, there is no telling how much further the temple extends underwater.

Thirdly, its perfectly smooth, perfect angled flanks, in contrast to the staired designs of Kobold and Lizardfolk temples, are made of seamless and flawless Ebonstone. This is an extremely rare and exceedingly resilient type of mineral known for being jet black, virtual imperviousness to heat or cold, and incredible durability rivalling that of Adamantine. Some scholars believe it may be a single, gargantuan piece. This calls its origins into question even more, as even the greatest master stoneworkers of the Dwarves are incapable of such precision on such a scale.

And lastly, there is an area with a diameter of several miles centered on the temple where temperatures suddenly plummet, covering the entire lake and its shores. This cold deepens as one ventures closes to the temple down to near freezing at the base. The sweltering heat and dense vegetation of the surrounding jungle suddenly stop at the edge of this area and animals take a detour around it. No weather, not wind or rain, affects it. It effectively makes Agon Lake seem a fell, lifeless place. Oddly enough, adventurers and explorers remark that while it is cold, there is no malice spreading from it but an atmosphere of serene stillness, as if time simply slows down and then finally stops starting from the edge.

The top floors were once inhabited by a Black Dragon, which moved out after it began growing too large and found the temple too cold for comfort. The floors above water level can be accessed normally, but those below are seemingly flooded with icy water. When the Dragon departed, it left behind a book called The Bloodline of Archaeon the Dread. The Philosoraptor has expressed an interest in this tome and asked the party to retrieve it for him in exchange for access to his vast knowledge. Rumor has it there are many more treasures to be found within.

Addendum: After a grueling struggle facing the many challenges of Agon Temple, the party discovered tombs containing Chozo skeletons and that the massive building is most likely of their making. They unwittingly also activated the temple, causing it to lift its great mass off the ground up to a height of a little over 1,5 km, revealing its full size and shape. The building is not in fact a pyramid, but an octahedron about a kilometer high.