Hidden amongst the undulations of rock, the river splits in two. One of the branches winds out of the barren hills, and on to the sea. The other cascades down a cleft into the earth. Along its course a spray of plants has sprouted, starting with small grasses and flowers in tiny crevices. Just visible below, standing at the entrance, are the heads of small trees. Further down, in the deep, where the sediment of countless centuries has accreted, grows a vast subterranean forest. When night falls, the soft luminous glow of lichen lights the underside of spanning branches and thick vines. Through the caverns, birdsong burbles along below the splashing of water, and a soft, occasional snuffle permeates the undergrowth. No matter how still you are, no matter how long you wait, the only visible sign of life will be the twitching of leaves, and the sporadic staccato drip of water from the rock above makes even that suspect.