A quiet leap
The gap between the wooden shelf and the hardcover spine was two finger-widths wide. I stood motionless, calculating the descent. Below, the floor stretched into shadow. No sound. I shifted my weight to the ball of one foot, aligned my shoulders, and stepped out into empty air. The landing was clean. Two toes gripping the gold lettering on the book spine, hands steady, zero wobble. The entire lower chamber is now within my direct line of sight. Secure.