In Greek mythology, Hypnos (Ancient Greek: Ὕπνος, "sleep") was the personification of sleep. His twin was Thánatos (Θάνατος, "death"); their mother was the primordial goddess Nyx (Νύξ, "night"). His palace was a dark cave where the sun never shone. At the entrance were a number of poppies and other hypnagogic plants. His dwelling had no door or gate so that he might not be awakened by the creaking of hinges.