The Builder Temple sits near The Lost City's plaza. It is avoided by Sleestak, as it is not an Altrusian ruin but rather was built by some other humanoid culture. Outside the temple there are two very curious artifacts. The first is a large stone obelisk which Will Marshall suggested might represent the Pylons. The other is a stone tablet with mysterious markings that vaguely resemble letters of the English alphabet. Rick Marshall posited that there may be a possible connection.
Inside the temple is an empty antechamber with a sundial set into the floor, somewhat of an oddity since sunlight does not reach that far into the room. There is a solid stone door at the back, and at the top of the door frame is a sculptured relief high on the wall of two hands touching; one hand is convex, the other concave. The door only opens when the "right" individual puts his or her hand into the concave relief. Inside is an auto-illuminating chamber with a large Matrix Table. There are also several pieces of art including a chrome humanoid statue and a pane of hand-shaped glass.
When the chamber is explored by Cha-Ka, a glowing crimson red humanoid figure appeared in the Land. The figure was uninterested in Rick and Will, telling them "You have already proven yourself; it is not your time." When it encountered Cha-Ka and he faced the glowing figure. The figure morphed from a tall, featureless red humanoid into a boy - a more human-like twin of Cha-Ka - before vanishing. Cha-Ka was apparently left with a powerful ring and improved intelligence; at the end of the episode, he is shown playing music on a recorder that he had previously been unable to comprehend.
- After the episode "The Musician", the mystery of the Builders and their Temple was not explained further.