Superman-Red and Superman-Blue restore the bottle city of Kandor on New Krypton as part of their quest to complete all of Superman’s ‘Unsolved Super-Problems’, in Superman #162 (1963) by Leo Dorfman and Curt Swan.

DC returned to the Superman-Red/Superman-Blue premise in 1998, and the unshrinking of Kandor and New Krypton in 2008. Superman’s Unsolved Super-Problems became the Twelve Labors of Superman in Grant Morrison’s All-Star Superman.