Argo City is the birthplace and residence of Supergirl.
Argo City is a colony of Kryptonian settles who survived in a pocket of extradimensional space, with the help of a life-support system powered by a device called the Omegahedron. Zaltar borrowed it without the knowledge of the city government. However, after a mishap, the Omegahedron is blown into space. Supergirl travelled to Earth and after finally retrieving the Omegahedron from Selena, she returns it to Argo City and saves the populace.