In which valley did Israel's army camp facing Goliath and the Philistines?

Answer: Valley of Elah

The Philistines stood on one hill and the Israelites on another, with the Valley of Elah between them.

“Saul and the men of Israel assembled and camped in the Valley of Elah, arraying themselves for battle against the Philistines. The Philistines stood on one hill and the Israelites stood on another, with the valley between them. They are with Saul and all the men of Israel in the Valley of Elah, fighting against the Philistines.””— 1 Samuel 17:2-3, 17:19 (BSB)