"The area of effect is taller than it is wide, but you can fly out of it just as safely as running. Tell me when and I'll activate it."
Steel closes her eyes and droops, hovering to avoid falling over completely. "Oof. I can see why that's usually done by a team of three. The circle is active."
She feels a steadily increasing indescribable sensation, not corresponding to any of her senses.
And Steel stands vigilantly near the circle, idly practicing sorcery, eating once in a while, setting alarms each time she sleeps, but never moving more than fifty feet away.
Promise thinks about stuff. She made sure she had stuff to think about, but five days is kind of pushing it. She inspects the sensory deprivation itself, which is interesting for almost twenty minutes. Sigh.
After a while (who knows just how long), she can tell that there isn't quite nothing there. It's not light, or sound, or smell. Maybe it's harmonics. Whatever it is, it hovers teasingly on the edge of her perception, never quite making itself clear.
Meanwhile, Steel continues to vigilantly guard the stone circle, setting an immobilization-and-loud-sound trap around it whenever she is called by sleep or other needs.
Steel wakes up, determines the location of whoever set it off, and wreaths herself in a full-body force-shell shield before flying from the oak tree and dropping next to them from above. "Hello. My apologies for the spell, but I cannot allow anyone to cross this area."
"The noisemaker is the warning. This area is not safe to wander through unless you have taken the correct precautions."
"There's a stone circle nearby that traps whoever wanders into it. I'm trying to find a way to get my friend out of it and dismantle it, but meanwhile the best thing to do is keep others from blundering into the trap."
"Well, there is now. Trust me, you don't want to verify a malicious spell's existence yourself."
She walks to the circle, stopping a good five feet away.
"To the outer edge of the stones, and as tall as the trees here above and below it. I believe I will be able to extract her soon, but disabling the effect might take longer. I'm not going to leave it and let innocent fairies get trapped there helplessly, though."