The Earth is 4.5 billion years old. It has probably seen millions of volcanoes during its lifespan. Just over the last 10,000 years, about 1,500 have been active on land. Many more on the ocean floor remain unknown, according to the U.S. Geological Survey. The most famous volcanoes are in Hawaii, Italy and South America. Some are and dangerous, but accessible for hiking enthusiasts and adventurers. Japan, Indonesia, Philippines, Ecuador and Iceland are other countries widely known for their active and dormant volcanoes. But there are also places you may have never heard of, where lava lakes are hiding underground.