At the Temple at Williams

According to the Trevor Shaw's historical introduction to Cave Minerals of the World (Carol Hill ed., 1997), this 9th century BCE bronze relief is the earliest known depiction of a cave in art:

source [britishmuseum.org]

Taken from ornamental gates found at Balawat in Northern Iraq, this scene depicts the visit of Assyrian king Shalmanesser III to a cave near what was then believed to be the source of the Tigris river. It was an important location for the kings of Assyria, where the king "washed the weapon of Aššur", "made sacrifies to my gods", and "put on a joyful banquet". In the image, droplets of water fall from the ceiling, growing stalactites.

Recently, an even more surprising find has been made, giving credence to Scott Wolter's theory of Phœnician contact with the New World [jasoncolavito.com]. A bronze gate recently uncovered near the town of Williams, Oregon bears the following depiction of the discovery of Oregon Caves:

An inscription found on a stele nearby describes the scene:

Everything seemed to be leading me to the cave; for as I turned from my buck, I again found my dog with uplifted head and staring eyes directed into a clump of trees, waiting for the word "Go." I sprang for my gun and gave the word. He was off like lightning, while I followed as quickly as possible, and soon found myself in front of a large hole in the mountain. I could hear sounds of fighting coming from far back in the mountain. Undecided as to what to do, I stood waiting, when my dog gave vent to a weird, agonizing howl as if he were in great pain. Hesitating no longer, I rushed into the opening and soon found myself coming up against sharp crags on the wall. I soon decided it was a hard chase to pursue without a light and, thinking of a few matches that I had in my old fashioned shot-pouch, very soon had a light and, to my surprise, found I was in some sort of a save ; but losing no time in looking around, as the fight was being continued, I struck match after match, thinking I would soon be at the scene of the struggle. But no; my matches were gone! I turned to go back, but could see no rays of light. With the deafening howls and groans coming to my ears from somewhere near, made me think were I only out I would not attempt such a thing again. I finally found my way back to a running stream of water and, following it, came to the mouth of the cave. I waited anxiously for Bruno to come, and very soon he came splashing down the creek, and but for a few scratches was unhurt.

"History of the Discovery of the Marble Halls of Oregon"
in The Quarterly of the Oregon Historical Society, vol 23 no 3 [archive.org] pg 274-276
Elijah Davidson (1922)