After fighting wave after wave after wave of zombies, I have concluded that there's gotta be like two zombie dungeons in this one area.
And the worst part is, it's never just zombies. My kill count is now 5 skeletons, 10 zombies, 3 creepers, and there are two spiders still stalking me.
Along with at least three more zombies and another skeleton in a water/lava area below.