The Edge
From Tardis Wiki, the free Doctor Who reference
The Edge was a place in the Doctor's mind where each incarnation went before regeneration. It was represented to the Thirteenth Doctor by a barren cliff with a telephone pole. Here the Thirteenth Doctor interacted with the Guardians of the Edge, manifestations of her previous identites who maintained their own individual personalities while acting together as one being. (TV: The Power of the Doctor)