The Untempered Schism, not a Stargate.
The Untempered Schism is a gap in the fabric of reality, in which all young Gallifreyans must gaze into on entering the Time Lord Academy.
Some went mad gazing upon the Untempered Schism, some were inspired, and some ran away.
The Adjunct Professor looked into it as a young Gallifreyan and saw a penis. The Professor was deeply embarrassed and doesn't like to talk about the ordeal.