Armageddon is the place of the last battle. You’re thinking of apocalypse, which means unveiling that which was formerly hidden.
It’s in northern Israel. There are two battles in the ancient world at Megiddo, both involving the Egyptians. The second battle is the one John is likely alluding to in Revelation - a battle that ends the world, as it’s the battle that ended Josiah’s reign in Judah and essentially brought to an end the Davidic line of kings.