It was because when he crashed into the stone wall just now.
Ye Chenfeng was able to sense the thickness of this stone wall; as for those other stone walls he'd sensed before, he couldn't feel any end to them at all.
And judging from Ye Chenfeng's estimation, the thickness of this stone wall was roughly about one and a half meters.
Of course, it was also covered in all kinds of Runes. Wanting to break open this seemingly thinnest stone wall was probably not that easy either, but this stone wall was their only hope of leaving here.
Previously, there had also been Divine Emperor Realm experts from the Upper World bombarding this stone wall, yet now it was still completely intact, which showed just how strong this stone wall was.
