Wow, that was a lot more than I expected. The "debug room"-looking starting screen had me fooled for a bit, but the invisible walls piqued my curiosity. I didn't know I'd be playing this for so long!
My only suggestion would be to maybe make floor-tunnels easier to find? like, you have to be absolutely PARKED on those to actually fall through them.
I also made this map:
with more accurate labels. This helped a lot, and it was really fun charting this out and finding a reference point. I started with the endless rainbow pit, since I could easily see that looping on the left side of the map. Then I looked for where the entrances lined up and went from there.
All in all, wonderful experience.
Also, fuck the heart area.