Barn (The Day of the Doctor)

The Barn was a shed situated on Gallifrey that stood for at least 800 years. At least four known incarnations of the Doctor visited the barn at different points of their time stream.

During the Doctor's childhood, the Doctor would retreat to the barn to cry so that the other children wouldn't hear him. On one such occasion, Clara Oswald landed the TARDIS in the barn and comforted the Doctor as he slept, telling him the story of how he would return to the barn one day. TV : Listen

The Doctor would indeed return, this time in his unnamed War Doctor. Bringing with him the The Moment, which he intended to use to destroy Gallifrey, the Time Lords and the Daleks alike. However when the Moment manifested into Bad Wolf, she opened a portal to his future to show him the consequences of his actions.

The War Doctor returned from the future with the Moment ready to detonate. Soon after his arrival, the Tenth Doctor, Eleventh Doctor and a younger version of Clara Oswald arrived to assist him in Gallifrey's destruction. However the Moment showed them the direct consequences of their actions and the Eleventh Doctor decided to alter their plan.

The Barn, along with the rest of Gallifrey, was placed in a pocket universe after the 13 incarnations of the Doctor moved the planet to save it from destruction by the Daleks. TV : The Day of the Doctor