The Throne Room overlay consists of three pillars, curtain, steps and carpet. This turns the Indoor Background (sold separately) into a royal palace for David, a temple court where Paul preaches to the people, a visit to Queen Esther's banquet, and many others.
Background vs. Overlay:
Our backgrounds are a full scene, while an overlay is meant to be used in conjunction with a background. For example the Desert overlay covers up the water section of the Water & Sky background, so the sky is still shown above.