Board Thread:Questions and Answers/@comment-25069771-20140616130529/@comment-220364-20140619000603

And we've also had: IIRC none of the stories played up the Earthlings having problems.
 * Jack Knight visiting Krypton in the past
 * Lois visiting various Krypton-esque locations (Kryptonian gravity and red solar radiation), both pre and post Crisis.
 * Pre-Crisis Jimmy visited both Kandor in the bottle and Krypton in the past.