Thanks radiant and shirepirate.
I agree about the start checkpoint, just forgot about that one. Fixed above.
Skylight: Needed and intended for the outdoor area. Should not matter for the secrets, but due to the low precision (file size) it shines through the floor of one lower tunnel, I think. Not sure how to fix, but the secret passages are ugly anyway.
Those secrets are not shortcuts, as they are easy/boring to pass. It is meant just as a hidden extra, and they allow you to travel safely to some spots or t go back a bit without suicide. There's definitely more to find than "only dead ends".
All torches have sounds, but the settings are maybe poorly chosen. Some sections where you fall, e.g. near the start, do have windy sounds.
last vs finish checkpoint - doesn't finish kill you automatically? The player should have a chance to enjoy the view before starting another lap