I don’t know if others have found this hidden (intentional?) entrance to the Under Map, but I found it about 20 minutes ago, so I’d thought I would share. You will need a Wasp.
Update: The written instructions I provided were apparently a bit too hard to understand (which is understandable given that I could not provide screenshots or a video at the time). So here is a short 1 minute video with the location to the entrance.
Shttps://youtu.be/xVM26EIRXWE (remove the S at the beginning).
A word of caution: it is very easy to get lost, so stray from the entrance/exit at your own peril.
It would have been easier, true enough, but it was 2am when I found it, and I had no time to upload and download what clips I took. If the instructions make no sense to you, then I am sorry. As long as you can find the monument and the Propaganda Tower, you’re in the right area.
I will edit this post tomorrow with a link to a short video.