The Mysterious World of Caves and Caverns: Ancient Man's Home Sweet Home

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deep sea cave photo
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Caves can be found on every continent, within glaciers, and even, as seen here, under the oceans. Most simply, they are defined as a "natural underground space large enough for a human to enter."

Typically, a true cave has at least one portion that cannot be reached by natural light, though in common usage, a "cave" can include any opening into the earth.

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