Professor McGonagall entered Ravenclaw Tower in Deathly Hallows by correctly answering the eagle's riddle.
There was a genteel tap of the knocker and the musical voice asked, again, ‘Where do vanished objects go?’
‘Into non-being, which is to say, everything,’ replied Professor McGonagall.
‘Nicely phrased,’ replied the eagle doorknocker, and the door swung open.
Deathly Hallows - Chapter thirty - The Sacking of Severus Snape - Page 479 - Bloomsbury
Professor McGonagall is a Gryffindor.