Bates, Swan and Anderson have the Fortress of Solitude discovered in Action 407 (Dec. 71).
Superman is alerted when a small airplane crashes near the Fortress. He saves the man, and tends him st the Fortress before bringing him home. Superman does not realize that the crash was intentional, and the man was mapping the coordinates to the Fortress.
The story has a major subplot about the man’s teenage son, attempting to re-forge a bond between them. The son comes along on the father’s return trip, in the company of gangsters, just to be close with his father, not realizing the situation.
The gangsters bring Clark Kent along as a hostage, which allows lots of sneaking away to fight crime outside the Fortress action throughout the tale. We get told that one of the goons is in disguise, but that just slides by.
Luthor’s involvement isn’t revealed until close to the end, as he and the father get into a stand-off, and Lex kills the man.
Superman is a bit late in this one, but I guess it was fitting punishment for trying to find the Fortress in the first place.