Planet One
From Tardis Wiki, the free Doctor Who reference
Planet One was the first planet in the universe.
History
The Doctor decided to bring Amy there to see the oldest cliff faces in history, made of pure diamond, to decipher the writings on the face that up until then had not been translated. When they got there, however, the writing simply says "HELLO SWEETIE" and a set of temporal co-ordinates underneath, written by River Song who had teleported there, using a vortex manipulator she got from a blue-skinned alien called Dorium in The Maldovarium bar.
