Singing Towers

The Singing Towers of Darillium was where the Doctor spent what he knew would be River Song's last night with him. (TV: Forest of the Dead)

In what was orinally presented as the prelude to this final night together, the Eleventh Doctor also met a past version of himself on this night, when River went into the wrong version of the TARDIS. The younger Doctor asked his future self if this was to be the last time he would see River; the future Doctor replied, "Spoilers." (HOMEVID: Last Night)

In The Husbands of River Song, it is revealed that the Doctor has still not experienced their final night in his Twelfth incarnation as he kept putting it off. In the aftermath of a space ship crash on the planet, the Doctor tells a man searching for survivors to build a restaurant on the exact spot in front of the singing towers, and later attends dinner there with River. The Twelfth Doctor finally gifts River the sonic screwdriver that she will possess in Silence In The Library, and they spend their final night together, which on Darillium is 24 years.