The world's three deepest caves are all in Abkhazia and are: Krubera-Voronja Cave (2197 metres ), Sarma (1830 metres), Illuzia-Snezhnaja-Mezhonnogo (1753 metres). The fourth is in France: Gouffre Mirolda (1733 metres). The greatest depth, 2197 metres, translates to about 1.37 miles, a mere pinprick in the earth's surface -- the distance to the centre of the earth is 3,958.8 miles!

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