A commoner has run into a LOT of money! Unfortunately, everyone knows it. Good luck getting out of town in one piece!
The local lord has been deprived of his prize family heirloom, the thief isn’t exactly a thief, but rather an absent minded wizard. Get the heirloom from the kindly but absent minded professor. Simple, right? Well, except for the fine print.
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.