No, it's not that it's getting higher, but he realized that this palace and the outer space seem not to be on the same plane; this palace is like a world, and he is currently shuttling through the world's entrance.
Once he crossed the great doors of the Primordial Demon Palace, which is the threshold of this world, he looked up and was alarmed to find that the palace's gates were unimaginably high; if converted to the Tao Realm, it would likely be impossible to see the top of the doors.
He paused for a moment, then dashed into the palace.
The space changed in an instant, and in front of him lay a vast world. Within this Primordial Demon Palace, there actually existed another universe.
"The Primordial Demon Palace actually has a dual space. I've heard about it but never witnessed it myself. Today is the first time I'm seeing it."
