Darillium was the location of the Singing Towers. The Eleventh Doctor took River Song to see these towers the last time she saw him before she went to the Library and met the Tenth Doctor. She told the Doctor in the Library that "the last time I saw you - the real you, the future you, I mean - you turned up on my doorstep with a new haircut and a suit. You took me to Darillium to see the Singing Towers. What a night that was. The towers sang and you cried. You wouldn't tell me why, but I suppose you knew it was time. My time. Time to come to the Library. You even gave me your screwdriver. That should have been a clue." In the TARDIS the second version of the Eleventh Doctor told the first version of the Eleventh Doctor that he was taking River there and they discussed how it was her last meeting with them. (TV: Forest of the Dead, TV: Last Night)