Forgive me, my knowledge of this stuff isn't that great, but I remember hearing about or reading somewhere that for some period of time in Superman's life he decided to go live inside the core of the Sun for a very long time, is this correct? how much time was it?
That plot point is in the universe of the 12-issue mini-series All-Star Superman
in the regular continuity of the standard monthly Superman title.
Here's the summary of the story: All-Star Superman