Physikus

Relevance:
*) optical shop door -- not a realistic lock mechanism
*) thief's house lock -- that kind of high-tech lock is out of place in a slum,
   especially since it's visible
*) dock gate lock -- a strange place for a wall and gate, especially a high
   tech lock
*) orrery -- too contrived a setup to lock such a place

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Real-time:
*) optical shop door -- non-fatal, repeatable, not too easy since you have to
   do it three times in a row

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Reasonability:
*) dock gate lock -- the fundamental clue comes from the interface, telling you
   what section of the education content you should investigate; that section
   otherwise has no relevance to the challenge

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Difficulty:
*) orrery -- a long way from a very missable clue, and the clue has a clue to
   its relevance (the sun symbol is a clue to the relevance of the phases)