Question: where are all the hogwarts common rooms?
Answer: Gryffindor common room — located in Gryffindor Tower, through the Fat Lady's portrait.
Hufflepuff common room — located in Hufflepuff Basement, below ground level behind a stack of barrels near the kitchens.
Ravenclaw common room — located in Ravenclaw Tower, beyond a bronze eagle-shaped knocker that poses a riddle.