A TARDIS was stolen by the Twelfth Doctor and Clara Oswald on Gallifrey. After returning the Doctor to his own TARDIS, Clara and Ashildr stole this TARDIS and used it to travel around the universe.
History
After the Doctor plucked Clara away from her death by the Quantum Shade through the use of an extraction chamber, they retreated into the Matrix, where they were followed by the General, Ohila and Gastron. Clara distracted the Time Lords while the Doctor escaped, made his way to the workshop below the Cloisters where he had stolen his own TARDIS and stole this one. He then piloted it back in time a few minutes to materialize around Clara to rescue her.
They then took the TARDIS to the very end of the universe, where the Doctor found Ashildr waiting in a chair, a chessboard set up for when the Doctor arrived. They discussed the Hybrid, and Clara used the sonic sunglasses to listen in on the conversation. The Doctor later entered the TARDIS with Ashildr, and decided that Clara needed a memory wipe of him so that she could live a normal life again. Clara convinced him to make it completely random, and the Doctor ended up wiping his own memory of Clara. After he was unconsious, Clara piloted the TARDIS to Nevada, Earth, and dropped him off, before despositing the TARDIS nearby and disguising it as a North American diner. Later, the Doctor went in, and Clara, knowing that he didn't remember her, gave him a lemonade and had him tell the story of his adventures on Gallifrey.
When the story was done, Clara opened part of the wall and stepped back into the console room, where Ashildr was waiting. She told Clara she couldn't get the chameleon circuit working, so the TARDIS was stuck looking like a diner. Clara said that was "awesome," and decided that she needed to return to Gallifrey to be sent back to die as her death was a fixed point in time. However, as she was now effectively immortal, she decided that she had a little "wiggle room" and took off from Nevada, stating that their destination was Gallifrey, "the long way around", implying that Clara and Ashildr would use the TARDIS to have their own adventures before returning to Gallifrey.
Later, the TARDIS passed the Doctor's in space. (TV: Hell Bent)