There should be an option to have locked chest available for buying. The concept is quite simply that the player that lays such a chest can demand that a special password be enterred before the chest is opened and possibly he has the option to provide some descriptive text before it's opened (in order to provie a hint for example).
These chests could then be used for missions or generally for more interesting stuff.
In order to make them more interesting/rare (so that not everyone has them). Perhaps allow them to be bought only by benefactors or level 8 or more.
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