A spectacular sea of clouds enveloped Tianmen Mountain National Forest Park in Zhangjiajie, central China's Hunan Province, on Thursday, attracting crowds of visitors. Mist swirled through the iconic Tianmen Cave after rainfall, creating ideal conditions with abundant moisture and favorable winds. Known as Heaven's Gate, Tianmen Cave is a natural water-eroded cave at an altitude of over 1,300 meters, making it the world's highest natural mountain cave.