If there's a skull lock and you forgot your skeleton key, try working a beam of light into the mechanism.  Recall how "She springs a light, / Unlocks the door" (Dryden).  Similarly, "Morning with its key of light / Unlocks the dusky portals of the night" (Albert Laighton, Poems, 1878).  And "My light unlocks the stalls, / two dozen and one windows open— / all, except the window of the moon, / already painted on as shining" (Jane Shore, Eye Level, 1977).