A kingdom where, if there are multiple princes (princesses can't rule unless they have no siblings), the princes fight to the death in the arena to decide who gets to rule. A simple way to make sure your brother cannot make a bid for the thrown, and keeps the royal blood in one line.
The characters are given the task of transporting a flask of highly volatile liquid a long distance. The flask cannot be shaken too much or it will explode. The adventure involves stormy sea-voyages, bumpy cart rides through densely populated towns and horseback combat. In short there are many opportunities for it to break and explode.