That's right, Estraeah has a rope on her. If she falls, she can always use that to get back up. She pulls the rope as well as her adventurer's journal out of her bag, and with the light of her flashlight, flips to her page on knot tying. She reads it carefully; she knows that if she makes a mistake, it could lead to injury. She prefers to avoid upsetting Klaus again.
As if the thought somehow materialized him from thin air, she hears his voice as she finishes securing the rope around her waist. "Estraeah? God, what are you doing?"
She grits her teeth. "What does it look like I'm doing, Klaus? I plan to cross this gap in the floor!" She looks up to see him gawking at her.
"Uh, what gap?"
In disbelief, she whips around to show him the cavernous hole before her, but when she goes to do so, it is missing.
". . . huh." Perhaps she had imagined such a drop? No, definitely not. She directly shined her flashlight down to gauge the distance to the bottom. It was there, and now it is not.
This cave is, in fact, magic. Estraeah knew it had to be.