Sunken City of Altheras - Grand Cathedral

Altheras was a great sprawling city at the western base of the mountain ranges that bisects Talaruen and the Frozen North. It stretched for miles, roads criss-crossing the city in an intricate pattern.
At the heart of the city, towering above it all, was the Grand Cathedral. Built initially when the city was founded, and expanded upon multiple times as the city grew, it eventually became a massive sprawling city complex. Sages, Scholars, and Devotaries came from miles around, often even travelling for months, for an opportunity to learn and study here. Anyone admitted to learn and worship at the Grand Cathedral would be considered among the intellectual and spiritual elite of the times.
Historians cannot agree on what it was that caused the destruction of the Grand Cathedral and the surrounding city of Altheras. Many believe that the men and women that studied there became so arrogant that they refused to worship the gods, claiming they had knowledge equal to divinity. This caused the gods to sink the city for their arrogance. Others cite a great natural cataclysm that was not foreseen, and struck the city too quickly for it to recover from. A smaller band have a theory that those amongst the top echelons of the orders decided to sink the city themselves, although this is laughably dismissed in more reputable circles.
Nowadays, the entire city is sunk deep below the surface, and the surrounding countryside has become an impassable swamp. Many adventurers and treasure hunters dive into the sunken ruins of the city to recover gold and artefacts from the lost city. However, the Grand Cathedral itself, the largest physical structure of the entire city, has never been found. The swamp, now inhabited by many vile creatures, prevents any attempts to map it, and no record of the city layout survived whatever drove it beneath the ground.