Waters of Death

The Waters of Death is a great sea separating Uruk, where Gilgamesh lives, from The Far Away Place, which connects to Shurrupak, where Utnapishitm lives. Gilgamesh  and Utnapishitm crosses it every time they visit each other, and Urshanabi used them to travel to visit Utnapishitm to declare war on him. The waters were named because very few individuals have ever survived the journey across them, despite how many people have attempted it over the years.