Ключевые слова: adventure, ancient, asia, attraction, background, beauty, big, cave, cavern, dark, deep, destination, earth, entrance, formation, geologic, grotto, halong bay, hole, horizontal, inside, interior, landmark, landscape, light, limestone, mineral, mountain, mysterious, national, nature, no people, nobody, old, park, rock, rocky, speleology, stalactite, stalagmite, stone, tour tourism, tourism, tourist, travel, tunnel, underground, vietnam, wall, water,