The Thread of Sky (一线天, Yīxiàn Tiān) is a geological oddity that has been drawing visitors since the Song Dynasty: two massive rock faces have folded together into a narrow fissure, leaving a passage just wide enough for a person to squeeze through. The gap runs for about 100 metres, opening to a sliver of sky above. At its narrowest the walls are close enough to touch on both sides simultaneously.
The passage connects to a broader cave system in the cliff, and at the far end a shaft of light breaks through from above. The site is in the Lingyan Scenic Area of Wuyishan, a few kilometres from the Nine-Bend River. It can be combined with a visit to the nearby Lingyan Temple, one of the older Buddhist temples in the mountains, built into a cliff-face alcove in the Tang Dynasty. Mornings are quieter; the cave can be uncomfortably crowded on weekend afternoons.