Which of the following features is not available in all Planet Fitness locations?

The feature that is not available in all Planet Fitness locations is free towels. While many Planet Fitness gyms offer free towels as part of their amenities, this service is not universally provided across all locations. The decision to offer free towels can depend on a variety of factors, including the size of the gym, its membership demographics, and regional variations in service offerings.

In contrast, other features like massage chairs, 24/7 access, and group classes, while they may vary in availability depending on the specific facility, are more commonly integrated into the overall offerings at Planet Fitness gyms. Therefore, selecting free towels highlights the variability in available services, as it's not a standard feature that every location must provide, unlike the other choices listed.