Bare practice chamber off the saferoom, currently serving as a holding cell for one screaming head.
The training room is where Samantha has been parked, and from where her supernaturally loud voice carries all the way into the Saferoom without losing any volume. Carl finds her there alone: the re-animated severed doll head sitting face down in the middle of the floor, screaming, stopping the instant he walks in.
The room's emptiness is what makes the scene — nothing but bare floor between the door and the head, enough that she can roll herself across it to stop at his feet and look up. It is here that Carl kneels, sets her upright by her white hair, and cuts the deal that buys the household its quiet.
An empty practice chamber with bare open floor, adjoining the saferoom, with nothing in it at present but a severed head.
The party's practice space, repurposed as the isolation room for Samantha and the site of Carl's bargain with her.