Asgard

Asgard was a planet-sized theme park where the Eleventh Doctor and River Song once picnicked on 5 May 5147. (PROSE: Picnic at Asgard)

River recorded the adventure in her diary. (TV: The Husbands of River Song, Silence in the Library)

Behind the scenes

 * In Norse mythology, is one of the nine worlds, and the seat of the ruling aesir Gods of the Norse faith.
 * Asgard is also the name of a crater on Callisto, one of the moons of Jupiter.