I took a Dark Souls character into the Tomb of Giants before even ringing the second Bell of Awakening in order to get Rhea's miracles as early as possible. Bad idea. Severely underleveled I messed up the fight with her Hollow guards, accidentally aggroing the lady herself. So I had to venture back to Oswald to cleanse my sin, but the way up from the Tomb of Giants and Catacombs was just impossible to clear. Even if I had rescued Rhea successfully I probably wouldn't have made it back up, this is probably the hardest route in the game.

RIP that character.