Ключевые слова: abandoned, catacomb, cave, cavern, coal, construction, corridor, danger, dangerous, dark, deep, dig, dirt, dirty, dungeon, entrance, excavate, exploration, geology, industrial, industry, inside, interior, iron, light, limestone, lines, lining, mine, mineral, mining, mystery, old, ore, passage, prospecting, rail, railroad, railway, rock, rusty, shaft, sleeper, subway, tunnel, tunneling, underground, underpass, urban,