User blog comment:FairyRaven/Fairy Tail Chapter 365: Fairy in the Jail!, Review and Commentary/@comment-4449950-20131230024638/@comment-1359322-20131230162142

Seeing how Franmath was so surprised that Natsu found their HQ, Tartarus probably had put on a barrier or something to prevent mages to find them, so i don't think Cana can find them through Divination.

I guess i'm the only one who thinks that Tartarus' HQ itself is another Demon.