Taoists believe that the sacred mountains are interconnected via an underground network of dong tien, or grotto-heavens, with dong meaning to penetrate something and tien referring to heaven. Going back as far as the fourth century, grotto-heavens were places where heaven and earth touched. By entering a grotto-heaven you penetrate deep within the mountain and arrive in the world of immortals: you enter the beyond within. Mount Taibai has dozens of grotto-heaven. One of the grotto-heavens is called Place of Charm and Beauty (pinyin: Bieyou Dong Tien). Bieyou also refers to a celebrated poem Question and Answer in the Mountain by the great poet Li bai: You ask me why do I dwell in these green mountains / But I smile without a reply, only an easy mind / The river flows away silently / Bearing the fallen peach blossoms / Here is another world, but not the world of man. Peach blossoms refers to the legendary Peach Blossom Valley where deep in the mountains, in a different world, happy people (immortals) live who know nothing of our existence.