As Organization X was excavating this place back then, in order to cover up the secret, they planned to eliminate all the participants involved.
And these people knew what fate awaited them once the project was completed, so they secretly dug a few hidden tunnels during the construction, which was more or less what Xue Yin had described.
But this secret passage only leads to Experimental Zone No.1 from another direction. If you want to leave the underground laboratory, you still have to take the only elevator.
With the situation being urgent, there was no time to worry about that, so the three of them immediately headed to that secret passage following Ao Sai's map, and then toward Experimental Zone No.1.
Gu Fan thought for a moment and then decided to have Li Shi wait in Experimental Zone No.1, as he and Lin Xi needed to go back and find Su Hui; after all, they couldn't leave any companion behind.