Other activities included cave exploration, rock climbing and traversing coastlines, Mr Bradford added.

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The Blombos cave and the Diepkloof rock shelter in South Africa have turned up ostrich shells and pieces of ochre with ornate markings that date back 60, 000 years ago.

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Features include cave hamams (Turkish baths), rock-cut arches, walls patterned with volcanic colour-banding and panoramic terraces surveying the valleys.

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With views over Ortahisar village's rock castle of Swiss-cheese holes, and cave rooms that blend Ottoman antiques with funky and fun colour, the bohemian-chic Hezen Hotel is perfect for those seeking a splash of eclectic glamour in a boutique sanctuary.

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Their headlamps illuminate soda-straw rock drippings from the ceiling, and rippled flowstone on the cave walls.

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The air exiting the cave would be cooled by the thermal mass of the surrounding rock to within a degree or two of the yearly average temperature.

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The two sites were Jarama VI, a rock shelter not far from Madrid in central Spain, and Zafarraya, another cave, near Malaga on the southern Spanish coast.

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Jack Bradley Cave has only 15 milligrams of carbon per liter of water in the rock, the equivalent of 15 grains of sugar dissolved in a liter of water.

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