Boss Encounter Cavern

This enormous cave map led my players to a boss-like encounter. Taking place in The Shadow Plane, this cave is filled with undead and creepy statues. This map offers several dead ends, a hidden treasure room (my players did not find), and plenty of opportunities for mindless battle or clues to the greater storyline. What are these statues, for example? Perhaps each one has a clue, or perhaps they must be interacted with to open the door to the final room. The final room, on the bottom right, is designed for an important encounter, and holds important treasure.