Landing Platform 21 functioned as a docking location situated within Cloud City, which itself was located on Bespin.
During 4 ABY, a transport under the control of Doctor Shemza's contact within the Alliance was secured at the platform. Following Lando Calrissian's announcement, broadcasted via the city's intercom, regarding the Galactic Empire's presence, Shemza, Shorty, Rorworr, Galak, and Arani Korden engaged in combat to reach the platform and flee the now-occupied city.