Ages ago, a being of great power built an immense structure in the swamps today known as Mistmeer. No one remembers what that original structure was, or who owned it. The only thing anyone really knows, is that it was built on a place of power that continues to exist.
No one knows if the dungeon beneath the structure was designed by the same being, or someone who followed, but, as with all dungeons, adventurers came from near and far to extract its secrets and treasures. The dungeon was eventually cleared out, and those who pursued such goals moved on to other challenges.
The Ruins of Mistmeer, as they are called today, are less dangerous than they were, but they remain a place of power, calling out to creatures to settle in the protective recesses of its now empty dungeon.