お風呂

How it works

This uses the set pattern [noun] + に (to) + する (do, decide on) to mean "go with" or "settle on" something — literally "make it the お風呂(おふろ) (bath)". する (do) stays in its plain dictionary form, and the ？ (?) (a rising tone, no question word needed) softens it into a casual "shall we?" suggestion rather than a command.