In the episode haunted, Robin was fighting Slade in his mind. None of the other Titans really understood what was happening, so Raven used her powers to enter his mind and find out why he was acting so strangely.
posted over a year ago
and by going into his mind, Raven also found out a bunch of other stuff about him that he previously kept secret
In haunted Raven enters Robin's mind and she can see what he sees, feels what he feels and knows what he's thinking. He lets Raven in his mind. Now, Robin wants to get into Raven's to try and save her but Raven knows it's to dangerous so she says, "Robin, you know me better than anyone, you should know there are places in my mind you shouldn't go, where no one should ever go." By this I'm pretty sure she means she shouldn't even go those places in her mind herself.