Lin Chuan was not entirely in the dark about what was happening before him; the Taoist nun must have also been heading toward that secret realm.
Now that she had opened the entrance to the secret realm—though it was unclear how—this massive boulder was either a teleportation array or a mechanism guarding an entrance.
Recalling how the boulder had previously absorbed spiritual energy and Divine Sense, he guessed that opening the secret realm's entrance likely required a massive amount of spiritual energy as a sacrifice. The lifeless, desiccated corpse beside the boulder further confirmed this.
Chapter 310