Untempered Schism

The Untempered Schism was a natural opening in the space/time continuum, "a gap in the fabric of reality from which can be seen the whole of the Vortex". The Schism appeared to consist of an opening into the Time Vortex, contained in a circular ring. Before the Schism lay a plaque bearing the Seal of Rassilon.

The Untempered Schism played a vital part in the initiation of young Gallifreyan children who would then stare into the Vortex, starting them off onto their journey to becoming Time Lords. (TV: The Sound of Drums)

History
The Doctor noted on more than one occasion that it was direct exposure to the Time Vortex through the Untempered Schism that caused Gallifreyans to develop more quickly than other societies. Over "billions of years", it caused them to evolve into Time Lords. (COMIC: Old Girl, TV: A Good Man Goes to War, et al.) This was comparable to the way that having been conceived within the Time Vortex itself allowed the Silence to manipulate Melody Pond's biodata to make her into a proto-Time Lord capable of regeneration. (TV: A Good Man Goes to War) However, after he discovered information about the Timeless Child, suggested that the "noble creation myth" for regeneration that the Time Lords told themselves, according to which they had been "born to rule", had been a fabrication to cover up the sordid truth. (TV: The Timeless Children)

At any rate, later in their history, the Schism was used by the Time Lords in an initiation ceremony for children entering the Time Lord Academy. At the age of eight, the children would be taken to the Schism and forced to stare into it. (TV: The Sound of Drums) The Doctor and the Master agreed that the experience was painful, and both expressed a level of disgust at the idea of forcing a child into such an experience. (TV: The Sound of Drums, The End of Time)

When the Tenth Doctor's TARDIS brought him to ancient Gallifrey, billions of years before his time, he and Cindy Wu witnessed young Gallifreyans being forced into the schism by a group of Time Sentinels. (COMIC: Old Girl) During one initiation in the Dark Times, a group of students were thrown into the Schism. Their physical forms were splintered by unprotected travel through the Time Vortex. (COMIC: The Wishing Well Witch)

The Doctor said that, when subjected to the terrifying effects of the Schism even in his time, the children would react differently — "Some would be inspired, some would run away, and some would go mad". He identified himself as one of the ones who ran away and never stopped running. (TV: The Sound of Drums) One Time Lord historian treated the Doctor's three possibilities as a genuine classification, and suggested that others who ran away included his granddaughter Susan Foreman, Romana I, K'anpo Rimpoche, the First Drax, Azmael, the Corsair, and Outsiders such as Nesbin, Ablif, and Presta. (PROSE: A Brief History of Time Lords)

During the Master's initiation, he saw "the raw power of time and space". (TV: The Sound of Drums) It was at this moment that the Drumming, a signal sent back through time by the Time Lords in the final hours of the Last Great Time War, (TV: The End of Time) entered the Master's mind, subsequently plaguing him throughout the rest of his lives. (TV: The Sound of Drums) He interpreted it as a sign of fate, a "call to war", which set him on his bloodthirsty path. (TV: Last of the Time Lords)

According to the historian, those who were inspired were Savar, Runcible, Spandrell, Engin, Hilred, Kelner, Rodan, Maxil, Damon, Talor, Jerricho, Thalia, Hedin, Zorac, Flavia, Darkel, the Woman, the Partisan, Andro, Fabian, the General, and Androgar. Meanwhile, the Monk, the War Chief, Goth, the Rani, Morbius, Borusa, Salyavin, and the Visionary, were listed as having gone mad. (PROSE: A Brief History of Time Lords)

The Tenth Doctor described looking into the Schism as the first time any young Time Lord "saw eternity". (TV: The Sound of Drums) The book of A included the quote, "When I was young, I looked through eternity's eye, and eternity created me!" (PROSE: What Keeps Their Lines Alive)

When a temporal crisis rendered TARDIS travel all but impossible, the Twelfth Doctor, stranded on Gallifrey with Bill Potts, acquired a stash of Kyfred Gems and came up with the idea of using them to stabilise the temporal energy by throwing them into the Untempered Schism "like skipping stones". Bill accompanied the Doctor to the Schism, but had to wear a protective shield to avoid the sight of the Schism "melting her brain". (GAME: Lost in Time)

Behind the scenes

 * The "time tunnel" effect seen in the Untempered Schism, and reflected in the eyes of the young Master, is the same technique used in the opening title sequence of the Doctor Who TV series from series 1 to the 2009 specials and during certain episodes from 2005 onwards where the TARDIS is shown in flight through the vortex. It was also used at the opening of The Sound of Drums to represent the transit through the space-time continuum with Jack Harkness's vortex manipulator.