The Wonderbolts training compound is a large outdoors area encompessing both airspace and ground(cloud)space. It's located a ways off from the main hub of Cloudsdale, so that the Wonderbolts can train in peace. It houses training areas, equipment for the training of tricks, and spaces set aside for meditation. It also houses living quarters for all of the members of the Wonderbolts. It has a set of baths and showers to accommodate them.
The training compound may only be accessed by members of the Wonderbolts and their associates (i.e. Guards, Coaches, and Friends). Rainbow Dash once managed to sneak inside. After that event, the number of guards protecting the facility was doubled.
In case of emergency, the compound can serve as a shelter to anypony, and the Wonderbolts can be called out to serve as emergency guards.