I meant to say "pair of stand-alone WADs Final Doom" rather than "stand-alone pair of WADs Final Doom" in the review, I should have noticed it, but oh well.
❗️ Attention, spoilers. I recorded a video showing how to get to and deal with the secret zone: youtu.be/n-yrU4J4928. It is important to not lose the momentum after taking the jump pad, which leads to the platform, above which there is the arch with the secret teleporter. [writing in small to not let for eyes to be spoiled]
EDIT: I forgot to mention: when I turn around in that place (0:48 in the video), I always have an impression of seeing an arachnotron for a moment.
Anyway, @Spike congratulations on this level, this is the type of maps that I enjoy quite a lot in terms of gameplay, so I definitely appreciate this one!
Edited 15.03 minutes after the original posting.