Thanks a bunch for the detailed feedback! I really appreciate it. I'll keep tweaking it to try to improve it. Once you get the blue key, assuming the elevators are actually working like they should, you can jump off the platform where the key is and take an elevator back to the spawn. The blue door should be straight ahead from there. If the elevators are bugged (and there's a good chance of this, I've been struggling to fix a problem with them), there's a chance that you won't be able to get back up to the spawn area at all. If you can, though, here's where the door is:
Thanks for playing!