Singing Towers

The Singing Towers of Darillium was where the Doctor spent what he knew would be his last night with River Song. (DW: Forest of the Dead) The Doctor also met a past version of himself on this night, when River went into the wrong TARDIS. The younger Doctor asked his future self if this was to be the last time he would see River, to which the future self replied "Spoilers". (DW: Last Night)