When God opened his servant's eyes, what did he see filling the hills around Elisha?

Answer: Horses and chariots of fire

Elisha prayed, and the LORD opened the young man's eyes to see the hills full of horses and chariots of fire all around Elisha.

“When the servant of the man of God got up and went out early in the morning, behold, an army with horses and chariots had surrounded the city. So he asked Elisha, “Oh, my master, what are we to do?””— 2 Kings 6:15 (BSB)