I played this map three times, skill 0, 1, 0. Skill 1 because skill 0 contained some bugs Paul corrected. Skill 1 manageable for a slow player like me, skill 0 better to admire the wonderful architecture.
Remembering that I owned a MC Escher illustrated book long time ago I investigated the implementation of his art.
Even after long searching I could detect only 4 secrets including the thunderbolt. I couldn't puzzle out the secret with the pips (I had to google this, I'm from Germany), the eyes of a dice. Very clever. I'll give this another try after a break.
Great! An independent interpretation of Escher's art and a map full of suspense, thinking, shooting.
And, by the way, thank you also for "Derelict Freighter". I played this around one dozen times ....