Mega Mob Dungeons

This is a variant of the mob dungeon that is the antithesis of current mob dungeons. 

This dungeon is a mega structure with many rooms and 2-4 floors. There will be many spawners inside these mob dungeons, I'm thinking of 1 to 2 dozen. Spawners in this structure work very differently to spawners in regular mob dungeons. These spawners will spawn mobs at all light levels, only spawn a set number of mobs and turn off once they've reached their cap, have increased hardness so they are difficult to mine and are blast resistant. Rather than being out in the open, these spawners are hidden within the walls and floors. There will be lots of loot chests that are LOCKED (the chests can't be broken, moved or opened), and the chests will only open once you have broken all of the spawners. The spawners could drop keys if broken while still working, or it could happen through some kind of magic mechanism. There can be a large amount of generic, caving/mining related loot in this dungeon, but you can also find exclusive loot here (a unique banner pattern, a new music disk, the item that locks chests). I'm thinking that we could have all 3 types of spawners in this dungeon (spider, zombie, skeleton) and I think creeper spawners can be exclusive to this dungeon since the spawners would be blast resistant. This dungeon should be a place where we have epic battles against hordes of mobs and I think it would bring a greater emphasis on combat to the caving experience!