After defeating two factions of Daleks with the help of her friends, the Thirteenth Doctor suggested a visit to the Meringue Galaxy. As the Doctor explained to Yaz, Graham and Ryan, it was a restaurant which served meringue for every course, set down on furniture which was also made of meringue, and served exclusively by meringue waiters.
Graham and Yaz were excited to continue travelling with the Doctor to this destination, but Ryan opted to stay on Earth, his home. Graham decided to leave the TARDIS as well, wishing to spend this time with his grandson. (TV: Revolution of the Daleks)