Minecraft wiki entry for Defeating_a_monument, associated text: Your goal inside the monument is to take out the elder guardians to eliminate the Mining Fatigue III that hinders your ability to obtain the resources from the monument. There are three per monument: one in the "penthouse" at the very top and one in each of the wings flanking the main entrance. The elders themselves are not extremely difficult if you're prepared with strong armor and weapons, since they move and attack relatively slowly, but finding them within the maze can pose a challenge. It might help to wall off dead ends as you investigate them, and note that the wings are connected by a long hallway around the back of the monument that bypasses the maze. Alternatively, you could simply mine through the ceiling of the elder guardians' rooms with a high-level Efficiency pickaxe, to counteract Mining Fatigue.