Natural Wonder I Mud Vulcanoes I Azerbaijan

(CNN) - “This fire ha burned 4,000 years and never stopped, “ says Aliyeva Rahila. “Even the rain coming here, snow, wind - it never stops burning”

Ahead, tall flames dance restlessly a cross a 10-meter stretch of hillside, making a hot day even hotter.

Venetian explorer Marco Polo wrote of the mysterious phenomena when he passed through the country in the 13th century. Other Silk Road merchants brought news of the flames as they would travel to other lands.