I know them.
First one: In the second room part boxes where you jump up to go in the middle thing.
Second one: In the main part, near the high place where loads of nubs go, the boxes ou use to jump up.
3rd one: Next to the cage.
Have fun glitching,
Oh!
on the high place here everyone goes not the building thing but other end, use the ledge and corner glitch it, get behind the bars....