It brings to mind the science fiction novel Abduction
by Robin Cook where explorers find an ancient civilisation below the sea. Living so deep in the planet, the virtually immortal and way technologically superior inhabitants were safe from natural disasters that caused a series of mass extinctions throughout the ages. This caused them to be a very peaceful civilisation, of course, until present-day humans came to disrupt that serenity.
Despite how ludicrous the story turned out to be in the end, it is still a fascinating premise.
(Source: LiveScience)
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