Wen Mingyu explained to Su Xin in detail about the existence of the armory on Sky-Reaching Island, which surprised Su Xin. If it hadn't been for Xiao Huang mentioning it, he might have completely overlooked it.
The true armory of Sky-Reaching Island had been emptied out hundreds of years ago when it first emerged.
The only thing left behind by the old Sky-Reaching Sect is this immovable armory.
Moreover, the space inside the armor of Sky-Reaching Island carries various mysteries and phenomenons set by the people of the ancient Sky-Reaching Sect, it's anyone's guess how those were placed into that isolated space. However, the benefits of practicing cultivation in there are considerable.
Just as Xiao Huang said, it could help martial artists in the Divinity Transformation Realm to speed up their "The God Fuses with the Earth and Heaven," thereby aiding them in ascending to the Fusion God Realm.