Everyone dies. But delaying that impending sentence is the holy grail. Science, scorcery, and wishful thinking do all in their power to bestow such delays. Be your deeds pure or evil, cheating death is neither easy nor reliable.
Wanderers beware, these gates open not,
Except to those only who the way have bought.
You may purchase the right to pass me by,
By each guessing my riddles. Care to try?
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.