K how about digging up a password to an impregnable chest (even with future tech) that has a lock on it. The lock has a window of opportunity of a week to be opened with that password and that window comes around once every 200 years. The chest could have say, avant-garde research that even people don't have the balls to conduct and the research results could be something abso-bloody-lutely amazing like transmuting substances without using chemistry. A little cliche but there is plenty of room to change elements around to make it unique.
