Genuinely really enjoyed this! Very creative concept and well implemented, and I enjoyed the little touches of charm like how you can enter the paintings(?) on the walls. Reminds me of the Link Between Worlds zelda game on 3ds.
Some creative level design ideas, too - I really loved going under the carpets to evade the guards!
One suggestion I have is that if the gameplay is all about noticing tiny gaps, the object and wall graphics need to be simple enough that it's clear what's supposed to be a gap and what's not - sometimes I found small gaps in the brick walls that looked identical to ones you could actually go under, but they were probably unintentional as you couldn't pass through them haha. Maybe if you developed it further you could add unique "crack" textures/modelling to make the cracks/gaps a little clearer?
I also found the sound effects pretty funny - although the guard alert sound literally made me jump the first time it played ahahah.