Over which valley did Joshua command the moon to stand still?

Answer: Aijalon

Joshua said, "O sun, stand still over Gibeon, O moon, over the Valley of Aijalon" (Joshua 10:12).

“On the day that the LORD gave the Amorites over to the Israelites, Joshua spoke to the LORD in the presence of Israel: “O sun, stand still over Gibeon, O moon, over the Valley of Aijalon.””— Joshua 10:12 (BSB)