It looked like caves, like tunnels, and it felt deep. It took some time for this feeling to get down that we're thousands of feet below the earth's surface, and if something happens, there's probably no rescue.
We stayed there for over 2 hours (mostly walking from one place to the other), watching machines, the ore, the equipment, the workers, etc., accompanied by a super-experienced guide with decades of first-hand experience in coal, diamond, gold, and platinum mining.
It was a nice and memorable experience, good learning, and I'm glad that I went.
Me in the 'Level 763' safety suit, 763 meters deep down