Trenzalore

Trenzalore was a place that, according to Dorium Maldovar, would be where the First Question in the universe would be answered truthfully. The Doctor would arrive there at some point in his travels, at the fall of the eleventh. The religious order known as the Silence was determined to ensure that the Doctor never reached Trenzalore, as they greatly feared the answer to the question - because according to legend, when the question was asked, the Silence would fall. (DW: The Wedding of River Song)