Planet of the Hats

"" was a hypothetical planet that Donna Noble said she'd be ready for given the hat box she brought with her in the TARDIS. (TV: Partners in Crime)

At one point, Donna reminded the Tenth Doctor that they still had not travelled there. In response, the Doctor took her to the Planet of the Bats instead. (PROSE: A Short History of Everyone)

The Doctor, in his twelfth incarnation, claimed that such a planet did not exist, but Bernice Summerfield and Keri asserted that not only did it exist, but that they had visited it. (PROSE: Big Bang Generation)

Behind the scenes
Planet of the Hats appeared as an invalid location in the DWM 395 and DWM 425 instalments of Doctor Whoah!, where its people are always wearing hats and are hostile to those who are not. Its people see the destruction of hats as a criminal offence.