Stones that have been attuned to the extreme temperatures of deserts or icy wastes. Such stones are quite valuable to adventurers as they can use them in order to preserve or prepare meals, make extreme environments bearable, and use them in clever devices.
In a high canyon in the mountains, the players find a skeleton in a cage suspended from a pole. A few miles further, they find another, and a third contains a partially rotten corpse. The fourth contains a living man who looks as if he hasn't eaten in days. Turns out to be the local way of punishing criminals.