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You head up the stairs and reach the top after a short jaunt. It ends at a large, flat door that opens upward. You would have to push it. The doors are quite heavy, and you can manage it, but they may make a lot of noise.
If you have the Invisible, Inaudible Rock and would like to crush it now, swing by
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Or you can just smash the door open and head on out!
50 is your friend