For clarification, can all players of any level go to quest areas for the quest xp?
Players should be engaging in adventuring activities that provide some degree of risk to their characters. If a zone is no risk to the character, it's probably not a good adventuring site for that character. Yes, this means Epic Level Characters have a dwindling list of available adventure sites. Not all characters are created equal so there are not hard-and-fast level caps on areas, but if it seems like it's too easy, like it's a cakewalk, then it is too easy and the player should take their character somewhere else instead.
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