Ключевые слова: beautiful, beauty, bulgaria, bulgarian, cave, color, colorful, colour, colourful, deep, different, extreme, flowstones, gem, geology, horizontal, illuminated, inside, landmark, light, lighted, limestone, material, mountain, nature, onyx, rock, semiprecious, stalactite, stalagmite, stone, structure, tourism, travel, underground, venetsa, vivid,