The Spa Car is a train car that makes a minor appearance in the episodes "The Unfinished Car" and "The Musical Car". This car is just a regular spa with a sauna, a salt scrub, and most likely more typical spa treatments.

In Book One Tulip Olsen, One-One and Atticus traveled through this car, and spent some time there, before leaving and entering the Unfinished Car. Atticus did not find the car's treatments relaxing, informing Tulip that he felt that the human and corgi definitions of relaxation were very different.

In Book Three Grace orders the Apex kids to retreat into this car after they realize the car they were raiding, the Unfinished Car was going to move.