Determinant

The Determinant was an arena like area created by the Master from harnessing the powers of the psychic energy planet Siralos. Similar to the Matrix on Gallifrey, it was possible to create and shape any sort of situation, inhabitant or environment. Whilst abusing the powers of the planet, the Master was able to pit the Graak here against various games, puzzles, and traps in its efforts to save the first seven incarnations of the Doctor. The area was entered from the Great Divide. (GAME: Destiny of the Doctors)