The Keyboard Car is a car that appears in the episode "The Corgi Car." It is a car that appears to be in outer space with floating musical instruments and a piano pathway that leads from door to door which Tulip slides along.
This room was actually shown in the puzzle on Cartoon Network's website. Dropping on June 18, 2019, Cartoon Network posted a link on their social media accounts to a website displaying this room with the piano labeled and interactable. Upon playing the Infinity Train theme with cords D, B, G, & F#, the trailer played and gave us a first look at the series.