Over the centuries, the thieves, assassins and secret agents who operate within the underworld have come up with many ingenious devices for stealing and murdering, many of which are disguised well enough to be carried in plain sight.
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.