Dungeons can be found in caves because they only spawn connected to some kind of cave system. There is a chance that they can spawn with either one or two chests.
They can also spawn connected to abandoned mineshafts.
There is a fifty percent chance that the mob spawner will spawn zombies.
There is a 25 percent chance that it will spawn with a skeleton spawner.
There is a 25 percent chance one will spawn with a spider spawner.
If you want to find a dungeon, search through the cave networks in the game. There is no other place where you will be able to find one.
There is also a small chance of dungeon spawning without any chests.
