My initial thoughts were that this place is an ancient lizardfolk catacombs. In the northern end Yuan-ti were "mining" the tunnels for bones to create undead minions and guards. In the south was the crypt of a group of lizardfolk paladins, who even in death defend their ancestral burial site. And in the centre, a raider band of goblins and some hobgoblin/orc mercenaries had made their base.
In keeping with Caverns of Thracia, I attempted to have multiple entrances and ways down; a main staircase in the centre of the map is an evident entry to the catacombs, with a yuan-ti carved entrance in the north. To the north west is an aerie, the nest of a lrge bird (hard to see on the map as it looks just like any other cave wall), and there was a plan to have a disused well/air shaft lead into another part of the dungeon.
Stairs down are in the northern large hall, and the dark areas are chasms and fissures which all drop down.
Also the room to the east of the lake was meant to be a secret are, the resting place or prison of a devil. Inspired by this Dyson's map, at the bottom of this long shaft is a White Ziggurat, the prison of the Moronic Devil, held here by a chorus of other devils who siphon the power of the Moronic Devil.