The "Refugee" scenario.

Now it's clear, but what about the Astral Gate?

You can't get the Astral Gate anywhere except at the Altar of Magic Touch, which is located right behind this portal. As I said many years ago, this altar is easily mistaken for one of the rocks in the dungeon, so look carefully! So, jump behind the yellow one, see how this creature runs away from you right through the rocks, then quickly learn this spell and teleport behind it.