The Cave (2005)

Deep in the Romanian forest, a team of scientists stumble upon the ruins of a 13th century abbey. On further inspection, they make a startling discovery - the abbey is built over the entrance to a giant underground cave system. Local biologists believe the cave could be home to an undiscovered ecosystem, so they hire a group of American cave-explorers, led by brothers Jack and Tyler, to investigate its depths. But what they find deep inside the caves is not just a new ecosystem but an entirely new species altogether.

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