Athenia

Athenia was a colony city situated on the Moon.

The Twelfth Doctor and Bill Potts went to visit the Galatean duplicate of Alan Turing on Athenia to decipher the markings on the TARDIS. However, Alan had vanished two years previously. The Galatean Chiyoko, feeling her "mother" (the TARDIS' essence on Bill), had Bill take Chiyoko to the TARDIS, which Chiyoko could hear was screaming due to the markings on the TARDIS' shell. After reuniting with the Doctor, Chiyoko told him where to find Alan. They found Alan inside a replica of King's College, Cambridge on the Moon's surface. The arrival of the TARDIS caused the code, which was part of the Dreamspace-dwelling Phantom Piper, to make the Piper manifest through Alan using Block Transfer Computation.

When the Phantom Piper used Chiyoko's mind to create soldiers from every war to start a war between humans and Galateans. Bill told Maggie Cortez not to kill Chiyoko and told Maggie to trust the Doctor. With the help of a suggestion from the Doctor, Alan defeated the Piper by breaking down his code, allowing Chiyoko to live. (COMIC: The Phantom Piper)