"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
Another challenge? Getting up at 6:30 in the morning to go act. It's not fun acting that early in the morning or acting at 4 A.M in the middle of the night or in the morning when you're really tired. That's a challenge. What a luxurious problem to have.