During the Death Wars one unit was created filled with fanatics bearing unique tattoos that gave them an invaluable ability impressive in any military action: the ability to cheat death.
In the middle of a desert in an oasis is a single prospering oak tree. Near the tree is a large pool of water. Drinking from the water is said to give you eternal life but really only extends your life for as long as you continue drinking from it. Those that have found it and left, have never found it again. Some search for it still.