Mashu, as described in the Epic of Gilgamesh of Mesopotamian mythology, is a great cedar mountain through which the hero-king Gilgamesh passes via a tunnel on his journey to Dilmun after leaving the Cedar Forest, a forest of ten thousand leagues span. Siduri, the Alewife, lived on the shore, associated with "the Waters of Death" that Gilgamesh had to cross to reach Utnapishtim, the far-away.
The corresponding location in reality has been the topic of speculation, as no confirming evidence has been found. Jeffrey H. Tigay suggests that in the Sumerian version, through its association with the sun god Utu, "(t)he Cedar Mountain is implicitly located in the east, whereas in the Akkadian versions, Gilgamesh's destination (is) removed from the east" and "explicitly located in the north west, in or near Lebanon". One theory is that the only location suitable for being called a "cedar land" was the great forest covering Lebanon and western parts of Syria and, in consequence, "Mashu" is the whole of the parallel Lebanon and Anti-Lebanon ranges, with the narrow gap between these mountains constituting the tunnel. The word Mashu itself may translate as "two mountains", from the Babylonian for "twins". The "twins", in Semitic mythology, were also often seen as two mountains, one at the eastern edge of the world (in the lower Zagros), the other at the western edge of the world (in the Taurus), and one of these seem to have had an Iranian location.