Human: Write a detailed description of a foreboding cave in the wilderness with a slab, lichen, passage, and a chamber. Assistant: 
Heavy walls of rough-cut limestone blocks surround the low, dark vestibule, their surfaces etched deeply by thousands of years of seeping water, creeping lichen, and time. A huge slab of granite, now broken and fallen away from the entry it once sealed, lies at the exit to the moors outside, and a narrow passage leads into a larger chamber to the north.