Looking at what appear to be 90° angles where the walls join a mostly-flat ceiling, it seems more like a human-made tunnel than a natural cave to me. Are they sure no one was down there before, shaping it?
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"The Lady of the Lake, her arm clad in the purest shimmering samite, held aloft Excalibur from the bosom of the water, signifying by divine providence that this was some killer weed."
"The Lady of the Lake, her arm clad in the purest shimmering samite, held aloft Excalibur from the bosom of the water, signifying by divine providence that this was some killer weed."